KCommandBar: remove installed event filter in destructor
- Start Dolphin, Ctrl+Alt+I to invoked the KCommandBar
- Click "Close tab" (crash doesn't happen when you press Enter)
- Dolphin is being closed, KCommandBar is being torn down
- The eventFilter() tries to access d, which already have been destroyed down, which causes Dolphin to segfault and crash
This similar to the issue described here: https://blogs.kde.org/2021/02/20/uniqueptr-difference-between-libstdc-and-libc-crashes-your-application
The gist of it is, always remove all installed event filters on child widgets of the private class in the public class's desructor.
BUG: 452527 FIXED-IN: 5.94