This is really, really slow at the moment for a few reasons:
- it goes through the list of revisions twice
- it checks many more revisions than it needs to

Even after these improvements it's still by far the slowest audit so
am also making it a `--git` only audit.

Additionally, to further improve default `brew audit` performance do not
run `brew style` checks when doing `brew audit` with no arguments.

`brew style` can be run quickly and efficiently on all of a tap (and is
cached) so no need to duplicate it here.

We no longer use this and `hub checkout` does what we want better.

- add more detailed manpage section for external commands (more
  information moved from their READMEs)
- add `brew test-bot` to the manpage

This is deprecated in #7660.

Fixes #7516

Also remove default `--with-label` value and add `--without-approval`
option.

Reviews could be automatically dismissed on new commits pushed (there is
an option for that in repository settings on Github). That is not the
case for labels. They remain attached to a PR, even when new commits are
pushed. This is undesirable and creates security concerns, because
someone could introduce untested code just before the automerge happens.

Co-authored-by: Eric Knibbe <enk3@outlook.com>

Fixes #7320

Remove more unused code.

- remove Jenkins Testing support from `brew pull`
- update reference to MacStadium Orka
- remove reference to DigitalOcean

This will allow `brew style` and `brew audit` to be run separately
without providing duplicates.

Additionally, run RuboCop style rules when `--strict` isn't provided and
remove a confusing reference to `style`.

None of these made sense as end-user commands.

Co-Authored-By: Mike McQuaid <mike@mikemcquaid.com>