(partial cherry-pick) [AMDGPU] Remove unused includes (NFC) (llvm#116154)

Partial cherry-pick of be18736 for AMDGPUSplitModule.cpp

Change-Id: I768a5e8c5e944ab98712a996513a17e8695a0b30

Author: Pierre-vh

llvm/lib/Target/AMDGPU/AMDGPUSplitModule.cpp

@@ -46,22 +46,18 @@
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Module.h"
-#include "llvm/IR/User.h"
 #include "llvm/IR/Value.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/DOTGraphTraits.h"
 #include "llvm/Support/Debug.h"
-#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/GraphWriter.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Timer.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/Cloning.h"
-#include <algorithm>
 #include <cassert>
 #include <cmath>
-#include <iterator>
 #include <memory>
 #include <utility>
 #include <vector>