Revert of [proxies] Make Object.prototype.isPrototypeOf work with proxies.

src/prototype.h

Index: src/prototype.h
diff --git a/src/prototype.h b/src/prototype.h
index 2be43e4fbdc9d0794e8670938f709d77652d0387..072774985357110c23c01131e7e7b0a33fba39f4 100644
--- a/src/prototype.h
+++ b/src/prototype.h
@@ -106,20 +106,6 @@
     }
   }
 
-  // Returns false iff a call to JSProxy::GetPrototype throws.
-  // TODO(neis): This should probably replace Advance().
-  bool AdvanceFollowingProxies() {
-    DCHECK(!(handle_.is_null() && object_->IsJSProxy()));
-    if (!handle_.is_null() && handle_->IsJSProxy()) {
-      did_jump_to_prototype_chain_ = true;
-      MaybeHandle<Object> proto =
-          JSProxy::GetPrototype(Handle<JSProxy>::cast(handle_));
-      return proto.ToHandle(&handle_);
-    }
-    AdvanceIgnoringProxies();
-    return true;
-  }
-
   bool IsAtEnd(WhereToEnd where_to_end = END_AT_NULL) const {
     if (handle_.is_null()) {
       return object_->IsNull() ||