Fix circular require between webdrivers.rb and railtie.rb

[amatsuda]

webdrivers.rb requires webdrivers/railtie.rb, https://github.com/titusfortner/webdrivers/blob/161d1bb67fbf74638dcc82068cc6c002a7caed89/lib/webdrivers.rb#L7

and webdrivers/railtie.rb requires webdrivers.rb. https://github.com/titusfortner/webdrivers/blob/161d1bb67fbf74638dcc82068cc6c002a7caed89/lib/webdrivers/railtie.rb#L3

This causes warning: loading in progress, circular require considered harmful warning from the Ruby interpreter.

Here's a minimum step to reproduce.

$ ruby -w -rrails -rwebdrivers -ep
<internal:.../rubygems/core_ext/kernel_require.rb>:148: warning: <internal:.../rubygems/core_ext/kernel_require.rb>:148: warning: loading in progress, circular require considered harmful - .../webdrivers-5.0.0/lib/webdrivers.rb
    from <internal:.../rubygems/core_ext/kernel_require.rb>:149:in  `require'
    from <internal:.../rubygems/core_ext/kernel_require.rb>:160:in  `rescue in require'
    from <internal:.../rubygems/core_ext/kernel_require.rb>:160:in  `require'
    from .../webdrivers-5.0.0/lib/webdrivers.rb:7:in  `<top (required)>'
    from <internal:.../rubygems/core_ext/kernel_require.rb>:96:in  `require'
    from <internal:.../rubygems/core_ext/kernel_require.rb>:96:in  `require'
    from .../webdrivers-5.0.0/lib/webdrivers/railtie.rb:3:in  `<top (required)>'
    from <internal:.../rubygems/core_ext/kernel_require.rb>:148:in  `require'
    from <internal:.../rubygems/core_ext/kernel_require.rb>:148:in  `require'

This patch fixes the warning by simply removing the require call in webdrivers/railtie.rb, since there won't be any actual use case where directly requiring webdrivers/railtie.rb without requiring webdrivers.rb (via bundler in most cases).

[kapoorlakshya]

Thanks for your contribution!

P.S. Test failure is unrelated to your changes.