MediaPlayer test cleanup + new streaming test placeholder.

Removes unneeded annotations and clears compiler warnings. Since there are
already many MediaPlayer API tests in MediaPlayerTest, additional API tests
that we add (like the null stream location added in this CL) should be here.
New tests related to streaming should go in MediaPlayerStreamingTest.

Change-Id: I239930c058fabf65fb7c4e34af0c142255f59f32
3 files changed