This is based on the discussion at Homebrew/homebrew-core#91368.
A few reasons why we don't want to deprecate formulae that have
dependents:
1. This results in displaying warning messages to (at least some) users
that they can't do anything about.
2. `test-bot` does not test deprecated formulae, so we risk breaking
dependent formulae when one of its dependencies is not tested.
3. It is much harder to commit to a disable date for formulae with
dependents because we don't know when we'll be able to wean
dependents off of a deprecated formula.
I think it's important to have a disable date in mind when we deprecate
formulae. Otherwise, we might end up leaving formulae deprecated
indefinitely. This is bad because it teaches users to not take
deprecation warnings seriously.
