IR: Sink MDNode::Hash down to GenericMDNode::Hash

Part of PR21532.

llvm-svn: 222212
diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index b4da2e0..27ba9f7 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -140,7 +140,7 @@
 
 MDNode::MDNode(LLVMContext &C, unsigned ID, ArrayRef<Value *> Vals,
                bool isFunctionLocal)
-    : Metadata(C, ID), Hash(0) {
+    : Metadata(C, ID) {
   NumOperands = Vals.size();
 
   if (isFunctionLocal)