Calculating has_second_ref only once for single_ref context.

Change-Id: Ib1253e0606426850f53060a4c5303af86bf1c093
Removing vp9_findnearmv.{h, c} files.

Moving all code from that files to vp9_mvref_common.{h, c}.

Change-Id: Ibc4afcb8cea6847166ff411130e93611ebe63b20
Merge "Removing vp9_findnearmv.{h, c} files."
Merge "Calculating has_second_ref only once for single_ref context."