vp8: Fix to enabling MFQE

Remove the unused *_DEBUG_* enum values in vpx/vp8.h

This fixes issue with enabling MFQE, which was
caused in 4807f15, where the unused DEBUG flags
were removed from common/ppflags.h but not in vp8.h.

BUG=913246

Change-Id: I47f114ef20adc084cb4883add5ac3ebf58ae9f1d
1 file changed