Don't call preventDefault in the FocusGrid's click event

Calling preventDefault in the click event prevents buttons from handling the event.

BUG=455617

Review URL: https://codereview.chromium.org/879243007

Cr-Commit-Position: refs/heads/master@{#314911}

ui/webui/resources/js/cr/ui/focus_grid.js

@@ -67,7 +67,6 @@ cr.define('cr.ui', function() {
         row.makeRowActive(row.contains(target));
       });
 
-      e.preventDefault();
       return true;
     },
   };