[coverage] Removing emma after its deprecation cycle.
Review Request #3009 - Created Oct. 21, 2015 and submitted
pants 0.0.54 was just released and the deprecation messages here said we'd drop support in 0.0.55, so I'm removing emma here. This will ultimately be replaced by jacoco which picked-up where the emma project left off, but getting rid of this since nobody was using it anyway.
Manual coverage runs, ran integration tests, in ci now.