VideoFramePool: Remove unused methods

This CL removes requestNewBufferSet and setNotifyBlockAvailableCb
methods, that became unused after switch to C2BufferQueueBlockPool and
C2PooledBlockPool.

Bug: 268301611
Bug: 268305422
Bug: 270329448
Bug: 238710012
Bug: 238390060
Bug: 270331759
Bug: 238709912
Test: CtsMediaCodecTestCases
Test: CtsMediaDecoderTestCases
Test: CtsMediaV2TestCases
Test: GtsExoPlayerTestCases com.google.android.exoplayer.gts.CommonEncryptionDrmTest#cencSchemeTypeV*
Change-Id: I6085cb7d5a7118d2b81d1f6d9d533b98fc978fa1