transcoding: Rework MediaTranscodeManager test.

1. Remove MediaTranscodeManagerWithMockServiceTest and move
   all the tests to MediaTranscodeManagerTest.
2. Move the service died test in MediaTranscodeManagerTest into a
   seperate ServiceDied test as it affect the normal test when
   killing the service.

Bug: 160260102
Test: Unit test
Change-Id: I192200744a44d4d724289f6001255100b332c968
5 files changed