(maint) - Removed soon-to-be deprecated RSpec/FilePath cops

[gavindidrichsen]

Summary

This PR is a follow on from a recent puppet-lint PR to exclude the soon-to-be deprecated Rspec/FilePath and to favour the new Rspec/SpecFilePathFormat instead.

Additional Context

Since this cop is going to be deprecated in the next major release of rubocop >=3.0.0 according to the documentation, I've:

• added the deprecation at the end of .rubocop.yml to highlight that it is deprecated; and
• raised an issue to track and remove the exclusion when rubocop is upgraded >= 3.0. See https://github.com/puppetlabs/rspec-puppet/issues/81

Checklist

• [ ] 🟢 Spec tests.
• [ ] 🟢 Acceptance tests.
• [ ] Manually verified.