[analyzer] [NFC] [RetainCountChecker] Remove dead unused map

[NoQ]

I should have done this in D52804!

lib/StaticAnalyzer/Checkers/RetainCountChecker/RetainCountChecker.h

: public Checker< check::Bind,
                     check::RegionChanges,
                     eval::Assume,
                     eval::Call > {
   mutable std::unique_ptr<CFRefBug> useAfterRelease, releaseNotOwned;
   mutable std::unique_ptr<CFRefBug> deallocNotOwned;
   mutable std::unique_ptr<CFRefBug> overAutorelease, returnNotOwnedForOwned;
   mutable std::unique_ptr<CFRefBug> leakWithinFunction, leakAtReturn;
 
-  typedef llvm::DenseMap<SymbolRef, const CheckerProgramPointTag *> SymbolTagMap;
-
-  // This map is only used to ensure proper deletion of any allocated tags.
-  mutable SymbolTagMap DeadSymbolTags;
-
   mutable std::unique_ptr<RetainSummaryManager> Summaries;
 public:
   static constexpr const char *DeallocTagDescription = "DeallocSent";
 
   /// Track Objective-C and CoreFoundation objects.
   bool TrackObjCAndCFObjects = false;
 
   /// Track sublcasses of OSObject.
   bool TrackOSObjects = false;
 
   RetainCountChecker() {}
 
-  ~RetainCountChecker() override { DeleteContainerSeconds(DeadSymbolTags); }
 
   CFRefBug *getLeakWithinFunctionBug(const LangOptions &LOpts) const;
 
   CFRefBug *getLeakAtReturnBug(const LangOptions &LOpts) const;
 
   RetainSummaryManager &getSummaryManager(ASTContext &Ctx) const {
     // FIXME: We don't support ARC being turned on and off during one analysis.
     // (nor, for that matter, do we support changing ASTContexts)