calendar: Vertically center message icon rather than top-align it

... as requested by the designers.

https://bugzilla.gnome.org/show_bug.cgi?id=749958

js/ui/calendar.js

@@ -978,7 +978,6 @@ const Message = new Lang.Class({
         this._iconBin = new St.Bin({ style_class: 'message-icon-bin',
                                      y_expand: true,
                                      visible: false });
-        this._iconBin.set_y_align(Clutter.ActorAlign.START);
         hbox.add_actor(this._iconBin);
 
         let contentBox = new St.BoxLayout({ style_class: 'message-content',