Delete subsystem, Actuator and sensor assignment broken

[TechplexEngineer]

Steps to reproduce

1. Create a subsystem (Step 7)
2. Assign some sensors and actuators to it (Step 8)
3. Go back to (Step 7) and remove the subsystem
4. Go to Step 8 and notice how the dropdowns are now blank.

The dropdowns should go back to "Select a subsystem"