Fix handling of @removed APIs.

The @removed docs tag means that a particular API should be considered
as removed from the API surface area that it otherwise would have been
exposed through.

This set of CLs is fixing a bug where we @removed had been treated as
always removing from the public API.

Bug: 62341924
Test: make -j32 update-api
Change-Id: I336b2df4804e947a0b93a12269d6e7c5594eef7e