X11: don't block on a ConfigureNotify event during SDL_SetWindowBordered().

Unity's window manager is (legitimately, since it moves the client window's
position) sending one, and SDL was incorrectly trying to mask it out. Other
window managers (KWin, apparently) don't move the window and would hang here
indefinitely.

Fixes Bugzilla #3052.

src/video/x11/SDL_x11window.c

@@ -864,7 +864,6 @@ X11_SetWindowBordered(_THIS, SDL_Window * window, SDL_bool bordered)
 
     SetWindowBordered(display, displaydata->screen, data->xwindow, bordered);
     X11_XFlush(display);
-    X11_XIfEvent(display, &event, &isConfigureNotify, (XPointer)&data->xwindow);
 
     if (visible) {
         XWindowAttributes attr;