Fix compilation with gcc

Remove unused variable reported by gcc.

Change-Id: I02b37a41524d2c2d8e3ab1158bd0fd816c7124f1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3629601Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80387}

src/web-snapshot/web-snapshot.cc

@@ -1107,7 +1107,6 @@ void WebSnapshotSerializer::SerializeObjectPropertiesWithDictionaryMap(T dict) {
     if (!dict->IsKey(roots, key)) {
       continue;
     }
-    PropertyDetails details = dict->DetailsAt(index);
     WriteValue(handle(key, isolate_), object_serializer_);
     WriteValue(handle(dict->ValueAt(index), isolate_), object_serializer_);
     if (first_custom_index >= 0) {