js: Use Gjs GTypeName computation for all classes

As per previous commit we can remove the explicit GTypeName definitions
and use gjs auto computation for all the GObject registered classes.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/790

js/ui/shellMountOperation.js

@@ -44,7 +44,6 @@ function _setLabelsForMessage(content, message) {
 /* -------------------------------------------------------- */
 
 var ListItem = GObject.registerClass({
-    GTypeName: 'ShellMountOperation_ListItem',
     Signals: { 'activate': {} }
 }, class ListItem extends St.Button {
     _init(app) {