userWidget: Remove frame around avatar

There's a push for round user images, for which the existing square
frame is a bad match. So remove the frame and enforce the shape.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/811

js/ui/userWidget.js

@@ -18,7 +18,7 @@ var Avatar = class {
         this._user = user;
         params = Params.parse(params, { reactive: false,
                                         iconSize: AVATAR_ICON_SIZE,
-                                        styleClass: 'framed-user-icon' });
+                                        styleClass: 'user-icon' });
         this._iconSize = params.iconSize;
 
         let scaleFactor = St.ThemeContext.get_for_stage(global.stage).scale_factor;