[mips] Remove unused CondMov feature bit

Summary:
No functional change

Depends on D3675

Reviewers: vmedic

Reviewed By: vmedic

Differential Revision: http://reviews.llvm.org/D3676

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208410 91177308-0d34-0410-b5e6-96231b3b80d8