Hide competitor list for non-organizers before registration opens

[dunkOnIT]

Per discussion in #software-discussion:

• no reason for this to be visible before registration opens
• it displays accepted pre-registrations which is confusing
• removing this item could make the Register button more prominent

Great point from Tim Reynolds on Discord:

The logic can't be "if registration open date is in the future, don't show competitor list" since organizers can open a second registration period (eg registration closed two weeks before the comp but wasn't close to full, so they email wcat to change the registration start and end dates)
During the time between wcat changing the dates, and the new period opening, ideally the registration list would show

[dunkOnIT]

(Thought about whether this is still necessary with the new registration system - yes, because we're reverting a lot of the frontend components, and ideally we want auto-accept to be event-based as far as possible)