MediaPlayerWrapperTest: Remove unused TestLooperManager

This has the side effect of not blocking the Looper thread anymore, but looking at the code it seems to only be used for a timeout

Bug: 344658662
Test: m BluetoothInstrumentationTests
Flag: TEST_ONLY
Change-Id: I44c3632ce41e2c8e7b7a5fe073611e07926bb71f