Remove redundant comment in safe inline combine example

The comment on line 24 was redundant - the explanation about
allowObservableChange: false being the default was already
provided on line 18. Removed to avoid confusion.

Author: escamoteur

code_samples/lib/watch_it/multiple_values_inline_combine_safe.dart

@@ -21,7 +21,6 @@ class SafeInlineCombineWidget extends WatchingWidget {
         m.value2,
         (v1, v2) => v1 + v2,
       ),
-      // allowObservableChange: false (default) - selector called once, result cached
     );
 
     print('Widget rebuilt with sum: $sum');