Remove testMkvWithoutCueSeek test

The test file has key frames at 0, 1.92 and 5.96 seconds, and the test
does 3 seeks to 3000 ms, with flags SEEK_CLOSEST, SEEK_PREVIOUS_SYNC and
SEEK_NEXT_SYNC.
The SEEK_PREVIOUS_SYNC test expects a position greater than or equal to
5960 ms, which is wrong because the previous sync would be 1920 ms.
In addition, the SEEK_PREVIOUS_SYNC test is exactly the same as the
SEEK_NEXT_SYNC test, which doesn't make sense.

Bug: 143618626
Bug: 143347340
Bug: 141833958
Bug: 142298430
Test: build
Change-Id: If9161682824a8e6611167acb9dfdc405cc69d39b