Remove a bad string compare from r194968

  lib/Tooling/CompilationDatabase.cpp:275:34: warning: result of comparison against a string literal is unspecified (use strncmp instead) [-Wstring-compare]

This assert() should probably be fixed and added back at some point.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194969 91177308-0d34-0410-b5e6-96231b3b80d8