[ARM] Remove XFAIL on test/CodeGen/Generic/MachineBranchProb.ll

Summary: Refer PR23377. This test was XFAIL'ed for Hexagon as well as ARM. But it has now started passing for ARM.

Reviewers: hans, rengolin, aemerson, kparzysz

Subscribers: aemerson, llvm-commits, rengolin

Differential Revision: http://reviews.llvm.org/D14155

llvm-svn: 251652