[cleanup] Remove instanceof cache.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 3e5be95a7d758ccd484704dba27e673b2fa56f4c..3d4d9bd294f93bd95ae78c6c71249b1ef252458b 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -12557,7 +12557,6 @@ void SetInstancePrototype(Isolate* isolate, Handle<JSFunction> function,
       JSObject::OptimizeAsPrototype(Handle<JSObject>::cast(value));
     }
   }
-  isolate->heap()->ClearInstanceofCache();
 }
 
 }  // anonymous namespace
@@ -15283,7 +15282,6 @@ Maybe<bool> JSObject::SetPrototype(Handle<JSObject> object,
     DCHECK(!object->IsAccessCheckNeeded());
   }
 
-  Heap* heap = isolate->heap();
   // Silently ignore the change if value is not a JSObject or null.
   // SpiderMonkey behaves this way.
   if (!value->IsJSReceiver() && !value->IsNull(isolate)) return Just(true);
@@ -15351,7 +15349,6 @@ Maybe<bool> JSObject::SetPrototype(Handle<JSObject> object,
   DCHECK(new_map->prototype() == *value);
   JSObject::MigrateToMap(real_receiver, new_map);
 
-  heap->ClearInstanceofCache();
   DCHECK(size == object->Size());
   return Just(true);
 }