MuxerUnitTest:enable start/addtrack/stop tests

Uncommented some tests related to start/addtrack/stop sequences
that were failing. They are passing now that we are allowing empty
tracks in mpeg4 files.

Bug: 146423844

Test: atest android.mediav2.cts.MuxerUnitTest
Change-Id: Ic1b7908877b6d9c5ac95bb7931842c16577472ca
Merged-In: Ic1b7908877b6d9c5ac95bb7931842c16577472ca
(cherry picked from commit c144f1d0e9fc95d743fe7e3683be6881c7b61f08)
1 file changed