X11: isConfigureNotify() isn't used at the moment, comment it out.

src/video/x11/SDL_x11window.c

@@ -54,12 +54,12 @@ static Bool isUnmapNotify(Display *dpy, XEvent *ev, XPointer win)
 {
     return ev->type == UnmapNotify && ev->xunmap.window == *((Window*)win);
 }
+
+/*
 static Bool isConfigureNotify(Display *dpy, XEvent *ev, XPointer win)
 {
     return ev->type == ConfigureNotify && ev->xconfigure.window == *((Window*)win);
 }
-
-/*
 static Bool
 X11_XIfEventTimeout(Display *display, XEvent *event_return, Bool (*predicate)(), XPointer arg, int timeoutMS)
 {