Merge mediarouteprovider into mediaroutertest

By doing this, CTS and 'atest mediaroutertest' will not conflict.

Bug: 148768077
Test: atest mediaroutertest (w/o installing provider package)
      (after then) atest android.media.cts.MediaRouter2Test
Change-Id: I7479d362080f33ef7b44c6076143f46909762cb8