[LoopVer] Remove an assert that's redundant now. NFC

Ensuring that the PHI are all single-operand is not performed in the
second pass added by the previous pass.  This removes the assert from
the first pass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272650 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed