Revert "ffmpeg: Bring up Opus support."

Native Opus decoding depends on libavresample, which isn't currently provided.

Additionally, if/when this returns, it needs the Opus parser put in too.

This reverts commit 5f313cea4396f7aebe8dadf5f1781d0eaa21faa0.

Signed-off-by: Ian Leonard <antonlacon@gmail.com>