wayland: Remove surface() check in Window::setupWindowManagement()
At the moment, an Xwayland window can be marked ready for painting even though the corresponding wl_surface is missing. If that happens, Window::setupWindowManagement() will fail to create a plasma window and the task manager won't display the corresponding item.
As a short-term solution, remove the surface() check. It's not really needed after all. For example, if it takes too long to start an app or it doesn't show up at all, we still want to see a task manager item.
In long-term, kwin probably needs to take into account both xsync and whether wl_surface has been associated, which is more complex.