accel: support for accelerated frame threading

Don't set decoding to single threaded; FFmpeg now supports hardware
accelerated decoding with frame threading.

Change-Id: Icac21d2e79d3d5dda4660e8ac4f4fd0c465e66c4

src/media/video/accel.cpp

@@ -244,7 +244,6 @@ makeHardwareAccel(AVCodecContext* codecCtx)
                     codecCtx->get_format = getFormatCb;
                     codecCtx->get_buffer2 = allocateBufferCb;
                     codecCtx->thread_safe_callbacks = 1;
-                    codecCtx->thread_count = 1;
                     RING_DBG("Attempting to use '%s' hardware acceleration", accel->name().c_str());
                     return accel;
                 }