Remove more Requirement logic to enable future removal of default
formula logic. Also, output deprecations, convert symbol requirement
usage to deps and simplify the compatibility code for the direct
Requirement usage.
These are ones that were either already deprecated due to audit rules
or are just a simple `which` with a `default_formula` so should just
be a dependency.
Dependency is another similar, related class and it's super confusing
to have some Requirements that are named *Dependency.
ClosesHomebrew/homebrew#38891.
Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>