Remove unnecessary include.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@144210 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CodeGenModule.h

@@ -26,7 +26,6 @@
 #include "llvm/Module.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/StringMap.h"
-#include "llvm/ADT/StringSet.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/ValueHandle.h"