Bug: Subassembly does not clear when switching subsystems

[rahul-go]

It may seem to clear because the subassembly selection goes blank, but the frontend is still requesting the subassembly filter from the backend.

How to duplicate:

1. Select a subsystem
2. Select a subassembly
3. Select a different subsystem
4. Observe that the get request to the backend still contains the subsystem filter from the previous subsystem.