Remove obsolete copy headers

When LOCAL_COPY_HEADER lines are removed, we just removed the copy rule,
we didn't actually remove the old header, so C/C++ files could still
include the old headers during incremental builds.

While we do consider LOCAL_COPY_HEADERS as near-obsolet, and it'll
disappear as we move everything over to Soong, this could produce some
unfortunate incremental build results while people are attempting to
remove them.

Fix this by ensuring that only the files currently listed in
LOCAL_COPY_HEADERS exist in TARGET_OUT_HEADERS after we run Kati.

Test: Remove a LOCAL_COPY_HEADERS entry; see the header removed
Change-Id: I817305703a6996d50490d552623d7df019b608c9