Revert "Ignore double-removal of a connection"
Revert "Ignore double-removal of a connection"

This reverts commit 10d5e3214043e1c6bab5fd7e81c1933d8d144c45.

This does not fix the root cause, so the panic still happens.

<https://github.com/Genymobile/gnirehtet/issues/61#issuecomment-370772336>

Genymobile/gnirehtet,WPO-Foundation/gnirehtet,WPO-Foundation/gnirehtet,Genymobile/gnirehtet,Genymobile/gnirehtet,WPO-Foundation/gnirehtet,WPO-Foundation/gnirehtet