This is no longer used anywhere.

Fix various circular requirements, method redefinitions, etc.

It's really noisy and too pedantic for us to use now but I got it
working locally and used `--fix` to generate #3981 so let's add it as an
option for now.

and improve wording or formatting where necessary.

This matches the version that supports Ruby 2.3.3 syntax (which is the
version we use).

This requires updating to Rubocop 0.49.0 which will require some fixes
to rules, in Homebrew/brew and Homebrew/homebrew-core but opening this
for now so I remember.

This reverts commit 3e4547f5, reversing
changes made to 6edf9382.

Homebrew's actually ended up using a fair few gems. While we want to
avoid Bundler at runtime (and this PR still does that, in fact uses
Bundler even less at runtime than it did before) writing our own version
to use at build-time seems redundant.

This passed a symbol to `:except_cops` which caused a .

This avoids an error when RuboCop installed installed yet.

CC @GauthamGoli FYI.

Also refactor audit cops into two "departments"
 - FormulaAudit
 - FormulaAuditStrict

- Check if the JSON is definitely invalid (< 2 characters)
- Output the arguments that were passed to Rubocop