Delete tautological assertion.

After r256463, both the LHS and RHS now refer to the same variable. Before,
they referred to the member, the parameter respectively. Now GCC6's
-Wtautological-compare complains.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@288444 91177308-0d34-0410-b5e6-96231b3b80d8