Diagnostics: remove dodgy handler for bitcode inlineasm diagnostics.

Whatever crash it was there to present appears to have been fixed in the
backend now, and it had the nasty side-effect of causing clang to exit(0) and
leave a .o containing goodness knows what even when an error hit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@265038 91177308-0d34-0410-b5e6-96231b3b80d8