Handle case of pre-registered organizer/delegate being removed as organizer/delegate

[dunkOnIT]

Kevin raised the point of what should happen in the case that an organizer/delegate who has pre-registered for a comp is removed as an organizer/delegate.

It seems that what should happen is that their pre-registration is moved to Cancelled - check if WCAT agrees with this.

If so, there are two ways we could do this:

1. Have a trigger in the code that checks for pre-registrations when an organizer/delegate is removed, and automatically move the registration to Cancelled (theoretically possible, but might be hard to implement)
2. Raise an error when trying to remove an organizer/delegate if they have a non-cancelled registration and registration hasn't started yet[1]

[1] We can use the same logic we're drafting to decide whether or not to display the "Competitors" tab to determine this, so that we don't run into the issue of this causing problems when there is a second registration period