[Object][XCOFF] Remove extra includes from XCOFF related files. [NFC]

[sfertile]

Summary

Removes a number of includes where the included file was either not needed, or already included from ObjectFile.h

[DiggerLin]

LGTM

llvm/trunk/include/llvm/Object/XCOFFObjectFile.h

 //===- XCOFFObjectFile.h - XCOFF object file implementation -----*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the XCOFFObjectFile class.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_OBJECT_XCOFFOBJECTFILE_H
 #define LLVM_OBJECT_XCOFFOBJECTFILE_H
 
-#include "llvm/ADT/StringRef.h"
-#include "llvm/ADT/iterator_range.h"
-#include "llvm/BinaryFormat/Magic.h"
 #include "llvm/BinaryFormat/XCOFF.h"
-#include "llvm/MC/SubtargetFeature.h"
-#include "llvm/Object/Binary.h"
-#include "llvm/Object/Error.h"
 #include "llvm/Object/ObjectFile.h"
-#include "llvm/Object/SymbolicFile.h"
-#include "llvm/Support/Casting.h"
-#include "llvm/Support/Error.h"
-#include "llvm/Support/FileSystem.h"
-#include "llvm/Support/MemoryBuffer.h"
-#include <cassert>
-#include <cstdint>
-#include <memory>
-#include <system_error>
 
 namespace llvm {
 namespace object {
 
 struct XCOFFFileHeader32 {
   support::ubig16_t Magic;
   support::ubig16_t NumberOfSections;
 

llvm/trunk/lib/Object/XCOFFObjectFile.cpp

 //===--- XCOFFObjectFile.cpp - XCOFF object file implementation -----------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the XCOFFObjectFile class.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Object/XCOFFObjectFile.h"
-#include "llvm/ADT/ArrayRef.h"
-#include "llvm/Support/BinaryStreamReader.h"
-#include "llvm/Support/Endian.h"
-#include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/MathExtras.h"
 #include <cstddef>
 #include <cstring>
 
 namespace llvm {
 namespace object {
 
 // Checks that [Ptr, Ptr + Size) bytes fall inside the memory buffer
 // 'M'. Returns a pointer to the underlying object on success.