statusMenu: Don't force a screen lock when suspending

The screen panel in System Settings has a preference whether the
screen should be locked on suspend. This works fine when suspending
by closing the lid, but the "Suspend" menu item in the user status
menu ignores the setting and always locks the screen.
Fix by activating the screen saver before suspending rather than
locking explicitly.

https://bugzilla.gnome.org/show_bug.cgi?id=652327