Delete User::dropHungOffUses and move it in to ~User which is the only caller. NFC.

Now that the subclasses which care about hung off uses let ~User clean it up,
there's no need for a separate method.  Just inline it to ~User and delete it.

Reviewed by Duncan Exon Smith.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239491 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/Instructions.cpp

@@ -93,10 +93,6 @@ PHINode::PHINode(const PHINode &PN)
   SubclassOptionalData = PN.SubclassOptionalData;
 }
 
-PHINode::~PHINode() {
-  dropHungoffUses();
-}
-
 // removeIncomingValue - Remove an incoming value.  This is useful if a
 // predecessor basic block is deleted.
 Value *PHINode::removeIncomingValue(unsigned Idx, bool DeletePHIIfEmpty) {
@@ -190,10 +186,6 @@ LandingPadInst::LandingPadInst(const LandingPadInst &LP)
   setCleanup(LP.isCleanup());
 }
 
-LandingPadInst::~LandingPadInst() {
-  dropHungoffUses();
-}
-
 LandingPadInst *LandingPadInst::Create(Type *RetTy, Value *PersonalityFn,
                                        unsigned NumReservedClauses,
                                        const Twine &NameStr,
@@ -3325,10 +3317,6 @@ SwitchInst::SwitchInst(const SwitchInst &SI)
   SubclassOptionalData = SI.SubclassOptionalData;
 }
 
-SwitchInst::~SwitchInst() {
-  dropHungoffUses();
-}
-
 
 /// addCase - Add an entry to the switch instruction...
 ///
@@ -3450,10 +3438,6 @@ IndirectBrInst::IndirectBrInst(const IndirectBrInst &IBI)
   SubclassOptionalData = IBI.SubclassOptionalData;
 }
 
-IndirectBrInst::~IndirectBrInst() {
-  dropHungoffUses();
-}
-
 /// addDestination - Add a destination.
 ///
 void IndirectBrInst::addDestination(BasicBlock *DestBB) {