[NFC] Minor cleanup for ValueHandle code.

[varungandhi-apple]

Summary

Based on feedback in https://reviews.llvm.org/D93433.

[dblaikie]

Looks good, thanks!

llvm/include/llvm/IR/ValueHandle.h

 public:
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
   AssertingVH() : ValueHandleBase(Assert) {}
   AssertingVH(ValueTy *P) : ValueHandleBase(Assert, GetAsValue(P)) {}
   AssertingVH(const AssertingVH &RHS) : ValueHandleBase(Assert, RHS) {}
 #else
   AssertingVH() : ThePtr(nullptr) {}
   AssertingVH(ValueTy *P) : ThePtr(GetAsValue(P)) {}
-  AssertingVH(const AssertingVH<ValueTy> &) = default;
+  AssertingVH(const AssertingVH &) = default;
 #endif
 
   operator ValueTy*() const {
     return getValPtr();
   }
 
   ValueTy *operator=(ValueTy *RHS) {
     setValPtr(RHS);

 /// a PoisoningVH ensures that an assert is triggered if looking up a new value
 /// in the map finds a handle from the old value.
 ///
 /// Note that a PoisoningVH handle does *not* follow values across RAUW
 /// operations. This means that RAUW's need to explicitly update the
 /// PoisoningVH's as it moves. This is required because in non-assert mode this
 /// class turns into a trivial wrapper around a pointer.
 template <typename ValueTy>
-class PoisoningVH
+class PoisoningVH final
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
-    final : public CallbackVH
+    : public CallbackVH
 #endif
 {
   friend struct DenseMapInfo<PoisoningVH<ValueTy>>;
 
   // Convert a ValueTy*, which may be const, to the raw Value*.
   static Value *GetAsValue(Value *V) { return V; }
   static Value *GetAsValue(const Value *V) { return const_cast<Value *>(V); }