Instrument monitor displays instruments and parameters that have been removed/closed

I have found that when we remove parameters from the our QCodes instruments, or close QCodes instruments, these instruments and parameters are still visible in the instrument monitor, even after the monitor has been updated and the parameters are no longer present in the snapshot.

For example, here I have run q0.close() to close the q0 instrument. Checking in the snapshot, we see that q0 is indeed no longer present

However, if we look at the instrument monitor, we see that q0 is still there, even after an update.

Furthermore, if I remove the parameters param_a and param_b of the meas_ctrl.experiment_data submodule using experiment_data.parameters = {}, we see that these parameters get removed from the snapshot, but are still there in the instrument monitor.

I think what's happening here is that when updating the instrument monitor, it goes through all the instruments that are in the snapshot and updates them. But it does not try to delete items from the instrument monitor which are not present in the snapshot. I think we should make sure that these items are deleted.