window-actor: Simplify the unredirected check in cull_out

https://bugzilla.gnome.org/show_bug.cgi?id=720631
compositor: Simplify the unredirected window management code

https://bugzilla.gnome.org/show_bug.cgi?id=720631
window-actor: Flip set_redirected around

I know it's confusing with the triple negative, but unredirected is how
we track it elsewhere: we have an 'unredirected' flag, and 'should_unredirect'.

https://bugzilla.gnome.org/show_bug.cgi?id=720631
window-actor: Remove old unused APIs

https://bugzilla.gnome.org/show_bug.cgi?id=720631