Remove empty non-virtual destructors or mark them =default when non-public

These add no value but can make a class non-trivially copyable. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234688 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/ValueMap.h

@@ -99,8 +99,6 @@ public:
   explicit ValueMap(const ExtraData &Data, unsigned NumInitBuckets = 64)
       : Map(NumInitBuckets), Data(Data) {}
 
-  ~ValueMap() {}
-
   bool hasMD() const { return MDMap; }
   MDMapT &MD() {
     if (!MDMap)