ci: remove trigger for `homebrew-cli` formula bump

[maxrake]

The trigger is no longer needed now that:

• The phylum-cli formula is included in homebrew-core
  • https://github.com/Homebrew/homebrew-core/blob/master/Formula/p/phylum-cli.rb
• The phylum-cli formula is included in the autobump workflow
  • https://github.com/Homebrew/homebrew-core/blob/master/.github/workflows/autobump.yml
  • https://github.com/Homebrew/homebrew-core/blob/master/.github/autobump.txt#L1011
  • This workflow runs once every three hours
  • It will automatically create new update PRs for outdated formula

Some documentation updates were made to be more consistent in wording.

Checklist

• [x] Does this PR have an associated issue (i.e., closes #<issueNum> in description above)?
  • See https://github.com/phylum-dev/roadmap/issues/409
• [x] Have you ensured that you have met the expected acceptance criteria?
• [x] ~Have you created sufficient tests?~
  • N/A
• [x] Have you updated all affected documentation?
• [x] ~Have you updated CHANGELOG.md (or extensions/CHANGELOG.md), if applicable~
  • N/A

[maxrake]

What's our transition plan for users that already have the CLI installed from our tap? Do we need to maintain both for a while?

The current plan is to keep the custom tap around for a little while longer, updating it (at least one more time) to follow the guidance from Homebrew Documentation on "Deprecating, Disabling, and Removing Formulae".

Using the disable! call is the preferred method since it will be the most obvious to users, but using the deprecate! call is also possible. In either case, a custom reason will be provided to make it clear that the tap should be swapped out for the homebrew core phylum-cli formula. Perhaps a link to the docs/README would be helpful so that a full set of "conversion" steps can be provided while the reason is kept short.

[maxrake]

The transition plan has been better outlined in this comment.

If that plan is acceptable, then this PR can proceed after the one to deprecate the custom formula is complete.

UPDATE: The custom phylum formula is now deprecated.