x11: Don't suppress slave mouse buttons when lacking keyboard focus

The window may not have keyboard focus when using remote control tools, so drop the keyboard focus requirement. Tested not to regress clickthrough suppression.

src/video/x11/SDL_x11xinput2.c

@@ -629,7 +629,7 @@ void X11_HandleXinput2Event(SDL_VideoDevice *_this, XGenericEventCookie *cookie)
                 /* Ignore slave button events on non-focused windows, as they can arrive before FocusIn events,
                  * or result in focus being incorrectly set while a grab is active.
                  */
-                if (SDL_GetMouseFocus() != windowdata->window || SDL_GetKeyboardFocus() != windowdata->window) {
+                if (SDL_GetMouseFocus() != windowdata->window) {
                     break;
                 }