Team number setter tool does not remove devices that are no longer present

[daltzctr]

Describe the bug
If it discovers a roboRIO once, it never removes it from the list, even if the roboRIO is powered on

To Reproduce
Steps to reproduce the behavior:

1. roboRIO turned on and connected
2. Team number setting tool connected
3. Confirm device appears
4. Disconnect roboRIO
5. Device never disappears, even pressing refresh

Expected behavior
The device to disappear

Screenshots
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