Don't clean obj/{APPS,JAVA_LIBRARIES} during installclean

Anything product specific in here should be caught by an explicit
dependency, or the command line changing. This drastically reduces the
build time after an installclean.

Before this change, we were re-running all dex2oat commands after each
installclean, even if nothing changed.

Change-Id: I9c735fe2c5d82109d56996021502319179e43671