Support all UnsupportedAppUsage annotations in processor

Add support for the libcore UnsupportedAppUsage annotation to
UnsupportedAppUsageProcessor. This is in order to make the two
annotations even more interchangeable.
Also take the opportunity to correct the documentation:
UnsupportedAppUsageProcessor no longer is involved in creating
greylist.txt, that functionality has been moved to
Class2Greylist.java in the art repository.

Bug: 130721457
Test: m framework-annotation-proc
Change-Id: I5cf1f97ca41349fc053315a2fd5bfd53a80ae128