Remove unused member variables from VP9_COMP

Removed three members from the VP9_COMP data structure:
inter_zz_count, gf_bad_count, gf_update_recommended.

These were part of the VP8 real-time mode implementation
that was removed from the initial VP9 codecbase.

Change-Id: I866b083b88ef02c74837277d50ce532ca88492f3