Fix some comments (#1606)

* Fix a comment

* Remove another comment

Author: Greg Soltis

Firestore/Example/Tests/Local/FSTQueryCacheTests.mm

@@ -273,11 +273,10 @@ - (void)testHighestListenSequenceNumber {
     [self.queryCache addQueryData:query2];
     XCTAssertEqual([self.queryCache highestListenSequenceNumber], 20);
 
-    // TargetIDs never come down.
+    // Sequence numbers never come down.
     [self.queryCache removeQueryData:query2];
     XCTAssertEqual([self.queryCache highestListenSequenceNumber], 20);
 
-    // A query with an empty result set still counts.
     FSTQueryData *query3 = [[FSTQueryData alloc] initWithQuery:FSTTestQuery("garages")
                                                       targetID:42
                                           listenSequenceNumber:100