[turbofan] Avoid redundant hash lookups in the broker.

This saves about 10% time in the initial copy of standard objects
in the TypeScript benchmark.

Bug: v8:7790
Change-Id: I2e725d43972db9598285f84fbba3c167cf8716b7
Reviewed-on: https://chromium-review.googlesource.com/1235657
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56080}

src/compiler/js-heap-broker.h

@@ -493,8 +493,6 @@ class V8_EXPORT_PRIVATE JSHeapBroker : public NON_EXPORTED_BASE(ZoneObject) {
   friend class ObjectRef;
   friend class ObjectData;
 
-  void AddData(Handle<Object> object, ObjectData* data);
-
   Isolate* const isolate_;
   Zone* const zone_;
   base::Optional<NativeContextRef> native_context_;