Reduce StringRef.h/Error.h includes to just the necessary STLExtras.h include and StringRef/Twine forward declarations
Remove unused Expected<> forward declaration
#ifndef LLVM_TOOLS_YAML2OBJ_YAML2OBJ_H
#define LLVM_TOOLS_YAML2OBJ_YAML2OBJ_H
-#include "llvm/ADT/StringRef.h"
-#include "llvm/Support/Error.h"
+#include "llvm/ADT/STLExtras.h"
#include <memory>
namespace llvm {
class raw_ostream;
template <typename T> class SmallVectorImpl;
-template <typename T> class Expected;
+class StringRef;
+class Twine;
namespace object {
class ObjectFile;