[ObjCARC][NFC] Fix defined but not used warning from D135041

[liaolucy]

try to fix defined but not used warning from D135041
llvm-project/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp:2486:6: warning: ‘void {anonymous}::ObjCARCOpt::releaseMemory()’ defined but not used [-Wunused-function]
2486 | void ObjCARCOpt::releaseMemory() {

|      ^~~~~~~~~~

[MaskRay]

LGTM.

llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp

 
 #ifndef NDEBUG
   void GatherStatistics(Function &F, bool AfterOptimization = false);
 #endif
 
   public:
     void init(Module &M);
     bool run(Function &F, AAResults &AA);
-    void releaseMemory();
     bool hasCFGChanged() const { return CFGChanged; }
 };
 } // end anonymous namespace
 
 /// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
 /// not a return value.
 bool
 ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
#ifndef NDEBUG
   }
 #endif
 
   LLVM_DEBUG(dbgs() << "\n");
 
   return Changed;
 }
 
-void ObjCARCOpt::releaseMemory() {
-  PA.clear();
-}
-
 /// @}
 ///
 
 PreservedAnalyses ObjCARCOptPass::run(Function &F,
                                       FunctionAnalysisManager &AM) {
   ObjCARCOpt OCAO;
   OCAO.init(*F.getParent());