Drop support for command line interface

[jamescooke]

Current issues

Command line interface causes some problems at the moment:

• It doesn't handle --aaa-act-block-style=large parameter right now. I would like to add a new piece of config called something like --act-return-variable to allow for custom naming of the result = variable that Flake8-AAA currently searches for, and I don't want to have to maintain it in two places.
• The main Checker class used by both the plugin and the command line needs to receive options from Flake8. At the moment we can't add typing for Flake8 specific args like option_manager because the command line doesn't install Flake8.
• Output from the command line isn't well structured or handled. Ideally we would use something like Rich / Textual to build a "better" test linting tool that captures some of the tutorial needs of #62 .

Expected behaviour / solution

In an attempt to speed up and streamline maintenance and development, will drop support for the command line interface.

Am happy to help anyone that wasn't to resurrect that functionality in a fork or new downstream version.