Remove KindleGen installation

[yahonda]

This pull request removes KindleGen installation KindleGen is not available for download.

https://www.amazon.com/gp/feature.html?docId=1000765211

KindleGen is no longer available for download. Please use Kindle Previewer to convert, preview, and validate your eBooks. Kindle Previewer provides the same functionality of KindleGen and, in addition, provides:

Fix #177

[fxn]

Does that Kindle Previewer support some kind of batch processing?

[yahonda]

I've found "Kindle Previewer" is not available for Linux, available for Windows and macOS as described below.

https://www.amazon.com/gp/feature.html?ie=UTF8&docId=1000765261

System Requirements • Windows 8.1 or later • Intel Mac OSX 10.13 or later

[yahonda]

Rails supports to generate the guide in EPUB since https://github.com/rails/rails/pull/45539 and deprecates guides:generate:kindle task. So I think we can safely remove KindleGen installation.

After https://github.com/rails/rails-dev-box/pull/202 is merged or installing pkg-config and libyaml-dev packages manually, rails-dev-box can generate the epub format guides follows.

• Steps to reproduce

• At Vagrant host git clone https://github.com/rails/rails-dev-box vagrant up vagrant ssh

• At rails-dev-box git clone https://github.com/rails/rails cd rails bundle install cd guides/ bundle exec rake guides:generate:epub

• Result

  $ bundle exec rake guides:generate:epub
  /usr/bin/ruby3.0 -Eutf-8:utf-8 rails_guides.rb
  Generating security.md as security.html
  Generating active_record_encryption.md as active_record_encryption.html
  Generating active_support_core_extensions.md as active_support_core_extensions.html
  Generating active_record_migrations.md as active_record_migrations.html
  Generating index.html.erb as index.html
  Generating generators.md as generators.html
  Generating action_controller_overview.md as action_controller_overview.html
  Generating action_mailbox_basics.md as action_mailbox_basics.html
  Generating command_line.md as command_line.html
  Generating rails_application_templates.md as rails_application_templates.html
  Generating active_record_multiple_databases.md as active_record_multiple_databases.html
  Generating action_text_overview.md as action_text_overview.html
  Generating 4_1_release_notes.md as 4_1_release_notes.html
  Generating 5_2_release_notes.md as 5_2_release_notes.html
  Generating routing.md as routing.html
  Generating active_storage_overview.md as active_storage_overview.html
  Generating association_basics.md as association_basics.html
  Generating asset_pipeline.md as asset_pipeline.html
  Generating api_app.md as api_app.html
  Generating webpacker.md as webpacker.html
  Generating active_job_basics.md as active_job_basics.html
  Generating active_record_basics.md as active_record_basics.html
  Generating plugins.md as plugins.html
  Generating 4_0_release_notes.md as 4_0_release_notes.html
  Generating 2_2_release_notes.md as 2_2_release_notes.html
  Generating 7_1_release_notes.md as 7_1_release_notes.html
  Generating active_record_querying.md as active_record_querying.html
  Generating i18n.md as i18n.html
  Generating action_mailer_basics.md as action_mailer_basics.html
  Generating active_record_postgresql.md as active_record_postgresql.html
  Generating 3_0_release_notes.md as 3_0_release_notes.html
  Generating 7_0_release_notes.md as 7_0_release_notes.html
  Generating action_view_helpers.md as action_view_helpers.html
  Generating maintenance_policy.md as maintenance_policy.html
  Generating configuring.md as configuring.html
  Generating autoloading_and_reloading_constants.md as autoloading_and_reloading_constants.html
  Generating error_reporting.md as error_reporting.html
  Generating _welcome.html.erb as _welcome.html
  Generating working_with_javascript_in_rails.md as working_with_javascript_in_rails.html
  Generating 2_3_release_notes.md as 2_3_release_notes.html
  Generating layouts_and_rendering.md as layouts_and_rendering.html
  Generating 6_0_release_notes.md as 6_0_release_notes.html
  Generating contributing_to_ruby_on_rails.md as contributing_to_ruby_on_rails.html
  Generating 3_1_release_notes.md as 3_1_release_notes.html
  Generating debugging_rails_applications.md as debugging_rails_applications.html
  Generating 6_1_release_notes.md as 6_1_release_notes.html
  Generating getting_started.md as getting_started.html
  Generating action_view_overview.md as action_view_overview.html
  Generating api_documentation_guidelines.md as api_documentation_guidelines.html
  Generating engines.md as engines.html
  Generating 5_0_release_notes.md as 5_0_release_notes.html
  Generating rails_on_rack.md as rails_on_rack.html
  Generating testing.md as testing.html
  Generating classic_to_zeitwerk_howto.md as classic_to_zeitwerk_howto.html
  Generating active_support_instrumentation.md as active_support_instrumentation.html
  Generating 4_2_release_notes.md as 4_2_release_notes.html
  Generating initialization.md as initialization.html
  Generating form_helpers.md as form_helpers.html
  Generating active_model_basics.md as active_model_basics.html
  Generating layout.html.erb as layout.html
  Generating development_dependencies_install.md as development_dependencies_install.html
  Generating upgrading_ruby_on_rails.md as upgrading_ruby_on_rails.html
  Generating 5_1_release_notes.md as 5_1_release_notes.html
  Generating action_cable_overview.md as action_cable_overview.html
  Generating 3_2_release_notes.md as 3_2_release_notes.html
  Generating threading_and_code_execution.md as threading_and_code_execution.html
  Generating active_record_validations.md as active_record_validations.html
  Generating ruby_on_rails_guides_guidelines.md as ruby_on_rails_guides_guidelines.html
  Generating caching_with_rails.md as caching_with_rails.html
  Generating _license.html.erb as _license.html
  Generating active_record_callbacks.md as active_record_callbacks.html
  Generating epub/welcome.html.erb as epub/welcome.html
  Generating epub/rails_guides.opf.erb as epub/rails_guides.opf
  Generating epub/toc.ncx.erb as epub/toc.ncx
  Generating epub/copyright.html.erb as epub/copyright.html
  Generating epub/toc.html.erb as epub/toc.html
  Generating epub/layout.html.erb as epub/layout.html
  => Using book dir: /home/vagrant/rails/guides/output/epub/OEBPS
  => Fixing filenames in Table of Contents
  => Using output dir: /home/vagrant/rails/guides/output/epub
  => Generating meta files
  => Generating EPUB
  => Done Generating EPUB
  Epub generated at: output/epub/ruby_on_rails_guides_c819075.epub
  $