ValueEnumerator.h - remove unnecessary includes. NFC.

The forward declarations are already present in the header.

upstream-commit: 3ae9957

Author: RKSimon

llvm/lib/Bitcode/Writer/ValueEnumerator.h

@@ -17,8 +17,6 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/UniqueVector.h"
 #include "llvm/IR/Attributes.h"
-#include "llvm/IR/Metadata.h"
-#include "llvm/IR/Type.h"
 #include "llvm/IR/UseListOrder.h"
 #include <cassert>
 #include <cstdint>