docs(ngEventDirs): update remarks on behavior

The event directives haven't stopped propagation by default in a long time.
If that behavior is desired, the handler may use the provided `$event` to call:

    $event.stopPropagation();

Closes #9640

src/ng/directive/ngEventDirs.js

@@ -33,10 +33,8 @@
    </example>
  */
 /*
- * A directive that allows creation of custom onclick handlers that are defined as angular
- * expressions and are compiled and executed within the current scope.
- *
- * Events that are handled via these handler are always configured not to propagate further.
+ * A collection of directives that allows creation of custom event handlers that are defined as
+ * angular expressions and are compiled and executed within the current scope.
  */
 var ngEventDirectives = {};