Remove all *bmc variables, which were used to record basic motion
search results (no advanced masked compound) when obmc and warped
motion modes were allowed to work with compound ref.
Remove switchable rate that is passed in to it, since in most
motion modes, we need to recalculate the cost based on motion_mode
and the refined mv. This change slightly improve the rd perf.

Performance change: -0.024%

Change-Id: I4afe0927e97cc7e7251022957f7665ed3032079c