Disable building coverage with javac

Emma is unable to process framework.jar, and making framework
classes.jar depend on the emma output causes builds to fail when
emma is enabled.  Make classes.jar depend on the jarjar output
instead, bypassing emma for now.

Test: m -j EMMA_INSTRUMENT=true EMMA_INSTRUMENT_FRAMEWORK=true check-public-api
Change-Id: I861282292816e29ca27b67a3eef978d951c1a4dc