More comment fixes (#3649)

Author: schmidt-sebastian

firebase-firestore/src/main/java/com/google/firebase/firestore/local/QueryEngine.java

@@ -105,7 +105,7 @@ public ImmutableSortedMap<DocumentKey, Document> getDocumentsMatchingQuery(
    */
   private @Nullable ImmutableSortedMap<DocumentKey, Document> performQueryUsingIndex(Query query) {
     if (query.matchesAllDocuments()) {
-      // Don't use index queries that can be executed by scanning the collection.
+      // Don't use indexes for queries that can be executed by scanning the collection.
       return null;
     }
 
@@ -153,7 +153,7 @@ && needsRefill(query.getLimitType(), keys.size(), previousResults, offset.getRea
       ImmutableSortedSet<DocumentKey> remoteKeys,
       SnapshotVersion lastLimboFreeSnapshotVersion) {
     if (query.matchesAllDocuments()) {
-      // Don't use index queries that can be executed by scanning the collection.
+      // Don't use indexes for queries that can be executed by scanning the collection.
       return null;
     }