a few clean-ups

1. remove prediction mode conversion
2. unified bmode, same for key and non-key frame
3. set I4X4_PRED count for pdf to 0, as I4X4_PRED is no longer
coded ever. It is determined by ref_frame and block partition

Change-Id: If5b282957c24339b241acdb9f2afef85658fe47d
16 files changed