Remove old -fdiagnostics-show-name option

This had no effect since the feature was removed in r150612.

I actually miss this option, maybe we can bring it back some day.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196782 91177308-0d34-0410-b5e6-96231b3b80d8