refactor(ngForm): Remove checking event.preventDefault and calling event.returnValue. Related to issue angular#4557. Worked with @bullwrinkle on this.

Author: shwei

src/ng/directive/form.js

@@ -471,9 +471,7 @@ var formDirectiveFactory = function(isNgForm) {
                   controller.$setSubmitted();
                 });
 
-                event.preventDefault
-                  ? event.preventDefault()
-                  : event.returnValue = false; // IE
+                event.preventDefault();
               };
 
               addEventListenerFn(formElement[0], 'submit', handleFormSubmission);