x11: Don't force position windows with an undefined position

[Kontrabant]

An undefined position means that the window manager can handle placement, so SDL shouldn't override that by forcing a position when showing a window.

Allows for removing a fair bit of now-unnecessary code as well.

Fixes #12060

[milq]

@Kontrabant, currently, my window does not center properly; instead, it remains positioned in a corner. This behavior is observed on my Debian 12 system with Xfce. I attach a video. Below is the code I am using, which is the default:

SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
{
    SDL_Renderer * renderer = NULL;
    SDL_Window * window = NULL;

    SDL_SetAppMetadata("Game", "1.0", "io.itch.milq.game");

    if (!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO)) {
        SDL_Log("SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) failed: %s", SDL_GetError());
        return SDL_APP_FAILURE;
    }

    if (!SDL_CreateWindowAndRenderer("Game", 1280, 720, 0, &window, &renderer)) {
        SDL_Log("SDL_CreateWindowAndRenderer() failed: %s", SDL_GetError());
        return SDL_APP_FAILURE;
    }

    // Etc.

Video: https://github.com/user-attachments/assets/bf218864-5595-48c9-8d72-fe1ad579b173

[Kontrabant]

SDL_CreateWindowAndRenderer() doesn't have parameters to set an explicit window position, so it is left up to the window manager to position the window. If you need the window in a specific position, you need to create a window with the position properties set. Forcing the window to center by default in this case was actually incorrect behavior.

[milq]

Okay, it's just that I thought SDL with SDL_CreateWindowAndRenderer centered the window by default. Thanks, @Kontrabant.