ACodec: Reduce the TWOmxNode wrapper in GraphicBufferSource

The wrapper of TWOmxNode introduced the extra binder calls to its
creator and got the chance to send back the same request to the original
requester. To avoid the redundant binder transactions, the patch simply
remove the wrapper by using the internal HAL interface.

Bug: 173502220
Test: Trace recording without redundant binder calls in emptyBuffer
Change-Id: I77ac10d12a15c4b07a37ac7e644400dba85a03a9