Make compiling an apex image explicit.

And when compiling an apex image, discard dex files not present
in an apex.

Test: m
Bug: 119800099

(cherry picked from commit c5e3a52473772a6aba3a8407b0151f6046c5e21b)

Change-Id: Iabbb7a479bd093c84c69d3d58884710f7a2f6823
Merged-In: Ie91c5b8d271783f04e4c1501f315a3ec59137475
4 files changed