river-status: fix output status destruction

There was a use-after-free if the Output was destroyed first, and the
memory of the output status was leaked.

river/Root.zig

@@ -203,6 +203,8 @@ pub fn removeOutput(self: *Self, output: *Output) void {
     // Destroy all layouts of the output
     while (output.layouts.first) |layout_node| layout_node.data.destroy();
 
+    while (output.status_trackers.first) |status_node| status_node.data.destroy();
+
     // Arrange the root in case evacuated views affect the layout
     fallback_output.arrangeViews();
     self.startTransaction();