display-x11: Unset tiled state if _GTK_EDGE_CONSTRAINTS is supported

display-x11: Unset tiled state if _GTK_EDGE_CONSTRAINTS is supported

Commit c415bef5de introduced support for the new _GTK_EDGE_CONSTRAINTS
atom. If the compositor supports that atom, however, we were always
setting the tiled state, even if no actual tiling information is
available, where the correct action is to completely remove any traces
of the tiled state.

Fix that by correctly removing the tiled state when compositor supports
_GTK_EDGE_CONSTRAINTS Xatom.

https://bugzilla.gnome.org/show_bug.cgi?id=788516