Remove unnecessary header include which violates layering

[GMNGeoffrey]

Summary

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

[GMNGeoffrey]

Update commit message

[TaWeiTu]

LGTM. Thanks for the quick fix!

[GMNGeoffrey]

Landing with failed builds. Looks like the same test is failing at HEAD: https://buildkite.com/llvm-project/llvm-master-build/builds/1281#df0e1b85-07a8-4199-8c41-79b6b38bd099

llvm/lib/Transforms/Utils/UnifyLoopExits.cpp

 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Utils/UnifyLoopExits.h"
 #include "llvm/ADT/MapVector.h"
 #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"
 
 #define DEBUG_TYPE "unify-loop-exits"
 
 using namespace llvm;
 
 namespace {