Add support for @removed tag.

@removed tags can be applied to packages, classes, methods, fields
that were once public API, but later removed. Things annotated by
@removed cannot be used by outside developers. But applications compiled
against the old API where the @removed API were still public should
continue to work and we must not delete the @removed APIs from the
source. This fix makes sure of that.

BUG: b/11293324

Change-Id: Iab3a8bdcaa0cb0742501c33e29b8121bc169bf1b
14 files changed