[analyzer][NFC] Remove the unused LocAsInteger::getPersistentLoc()

[martong]

LGTM. Are there any other getPersistentLoc function definitions in other SVals? Might they be also unused?

[steakhal]

In D125920#3524586, @martong wrote:

LGTM. Are there any other getPersistentLoc function definitions in other SVals? Might they be also unused?

IDK, might be.

clang/include/clang/StaticAnalyzer/Core/PathSensitive/SVals.h

 
 public:
   Loc getLoc() const {
     const std::pair<SVal, uintptr_t> *D =
       static_cast<const std::pair<SVal, uintptr_t> *>(Data);
     return D->first.castAs<Loc>();
   }
 
-  Loc getPersistentLoc() const {
-    const std::pair<SVal, uintptr_t> *D =
-      static_cast<const std::pair<SVal, uintptr_t> *>(Data);
-    const SVal& V = D->first;
-    return V.castAs<Loc>();
-  }
-
   unsigned getNumBits() const {
     const std::pair<SVal, uintptr_t> *D =
       static_cast<const std::pair<SVal, uintptr_t> *>(Data);
     return D->second;
   }
 
 private:
   friend class SVal;