Deprecate unused 'default' argument for magicwords

compat has a 'default' argument for each of the methods which
return a magic word.  It is now unused and deprecated in compat.
Use @deprecated_args to also deprecate it in core.

Change-Id: Ia600aed3fc43d950e9c98851029c20fd895a4438
Merge "Deprecate unused 'default' argument for magicwords"