The list of APUs on the main page and APUs in the system tree are not updated when a bitfile is removed

[rtzoeller]

The APUs shown in the list of APUs on the main page, as well as the APUs in the system explorer tree are not updated when a bitfile is removed.

• [ ] We should remove the APU section if no more RIOs are under it
• [ ] We should update the list of APUs whenever a bitfile is removed