UI: Remove unused RemoveSelectedSceneItem slot

Appears to be a remnant left by the undo/redo system changes, not used
at all by any parts of the UI. This slot does not have undo/redo
system functionality, so it is not useful in its current form.

UI/window-basic-main.cpp

@@ -3874,16 +3874,6 @@ void OBSBasic::RemoveSelectedScene()
 		api->on_event(OBS_FRONTEND_EVENT_SCENE_LIST_CHANGED);
 }
 
-void OBSBasic::RemoveSelectedSceneItem()
-{
-	OBSSceneItem item = GetCurrentSceneItem();
-	if (item) {
-		obs_source_t *source = obs_sceneitem_get_source(item);
-		if (QueryRemoveSource(source))
-			obs_sceneitem_remove(item);
-	}
-}
-
 void OBSBasic::ReorderSources(OBSScene scene)
 {
 	if (scene != GetCurrentScene() || ui->sources->IgnoreReorder())

UI/window-basic-main.hpp

@@ -660,7 +660,6 @@ private slots:
 
 	void DuplicateSelectedScene();
 	void RemoveSelectedScene();
-	void RemoveSelectedSceneItem();
 
 	void ToggleAlwaysOnTop();