Add Action Text uninstall to remove copied migration and files.

Hi folks,

I have been playing a bit with Action Text a lot lately and recently we have switched Action Text install to a generator in PR:

We could now use the generator to destroy the added files as well. Will it be a good idea to add a bundle exec rails action_text:uninstall to remove the copied files?

I would love to work on it and raise a PR if anyone is interested.

Thank you for your time!