ACodec: don't configure software encoders/decoders.

Not sure if this is correct in principal, but in practice every time
I have seen this called on a software dec/enc, it dies. I have also
seen multiple, stackoverflow queries that tring to create and
instance of MediaCodec (software dec/enc) fails, probably because
of what this fixes.

Change-Id: I4b6c02424fedf239462f22070f918929a9b8bf07