plugin_store: Remove unused code

This CL removes unused source code files, since classes inside of them
are no longer used in the component.

Removed classes are:
 * C2VdaBqBlockPool
 * C2VdaPooledBlockPool
 * H2BGraphicBufferProducer

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: I0fc53c942ecb44bde246fca72234a176acb47122
(cherry picked from commit 347ef462)