Revert "Popup window parent defaults to the first toplevel window"

This reverts commit e8e2c8175cfe269cdf94c0c47c70f27f3a033050.

Conceptually tooltips and context menus always have parent windows

src/video/SDL_video.c

@@ -1939,28 +1939,12 @@ SDL_Window *SDL_CreateWindow(const char *title, int w, int h, Uint32 flags)
 
 SDL_Window *SDL_CreatePopupWindow(SDL_Window *parent, int offset_x, int offset_y, int w, int h, Uint32 flags)
 {
-    if (!_this) {
-        SDL_UninitializedVideo();
-        return NULL;
-    }
-
     if (!(_this->quirk_flags & VIDEO_DEVICE_QUIRK_HAS_POPUP_WINDOW_SUPPORT)) {
         SDL_Unsupported();
         return NULL;
     }
 
     /* Parent must be a valid window */
-    if (!parent) {
-        /* Use the first toplevel window by default */
-        for (parent = _this->windows; parent; parent = parent->next) {
-            if (!SDL_WINDOW_IS_POPUP(parent)) {
-                /* Adjust the offset to be relative to this window */
-                offset_x -= parent->x;
-                offset_y -= parent->y;
-                break;
-            }
-        }
-    }
     CHECK_WINDOW_MAGIC(parent, NULL);
 
     /* Popups must specify either the tooltip or popup menu window flags */