telepathyClient: Fix fallout from Lang.Class port

this.parent was ported from calling the parent class's method like
MessageTray.Notification.prototype._init.call(this, ...);. When
porting to Lang.Class, the 'this' parameter is now passed automatically, but
removing it was forgot in a few places. Fix these places.

https://bugzilla.gnome.org/show_bug.cgi?id=665017