clients receive spurious xdg_toplevel configure events

Since commit f12697bb we sometimes send spurious reconfigure events to clients.

The easiest way I've seen to reproduce this is to start weston-subsurfaces, resize the window, then click in the green area.

After the resize (and not before!) the green area will redraw on every click, apparently due to receiving an xdg_toplevel configure event. This can also be seen with weston-terminal, where after a resize it will respond by updating its title bar (as viewed with WAYLAND_DEBUG=1)