Remove unnecessary header include which violates layering

This was introduced in https://reviews.llvm.org/D89774, but I don't
think it should be necessary.

Reviewed By: TaWeiTu, aeubanks

Differential Revision: https://reviews.llvm.org/D89843

Author: GMNGeoffrey

llvm/lib/Transforms/Utils/UnifyLoopExits.cpp

@@ -21,7 +21,6 @@
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/InitializePasses.h"
-#include "llvm/Transforms/Scalar/LoopPassManager.h"
 #include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"