Removed A2DP_GetTrackBitsPerSample() API because it is not needed

The A2DP_GetTrackBitsPerSample() API was replaced in the past
by A2dpCodecConfig::getAudioBitsPerSample() .
 * Removed A2DP_GetTrackBitsPerSample() and related codec-specific APIs:
   - A2DP_GetTrackBitsPerSampleSbc
   - A2DP_GetTrackBitsPerSampleAac
   - A2DP_GetTrackBitsPerSampleAptx
   - A2DP_GetTrackBitsPerSampleAptxHd
   - A2DP_GetTrackBitsPerSampleLdac
     NOTE: The removed A2DP_GetTrackBitsPerSampleLdac implementation
     had a bug: a2dp_ldac_caps.bits_per_sample -> ldac_cie.bits_per_sample
     This bug itself was uncovered when switching to clang-3960126
   - A2DP_VendorGetTrackBitsPerSample()
 * Replaced few leftover usages of A2DP_GetTrackBitsPerSample()
   A2dpCodecConfig::getAudioBitsPerSample()
 * Updated the unit tests

Test: Code compilation, unit tests, A2DP streaming
Bug: 37752547
Change-Id: I7feeda0f32922b8ef888b157673e3e2ade98b179