hide “Deactivate now” button once deactivated

[as6325400]

Fixes https://github.com/DOMjudge/domjudge/issues/2687

Use getDeactivatetime() to check whether the Deactivate time field is set, and decide accordingly whether to display the Deactivate now button.

[nickygerritsen]

Now the button doesn't show if a deactivate time is set, even if it is in the future. Is that what we want? I'd say we only hide it if the deactivate time is in the past?

[as6325400]

Now the button doesn't show if a deactivate time is set, even if it is in the future. Is that what we want? I'd say we only hide it if the deactivate time is in the past?

Sorry, I didn’t notice that—thanks for pointing it out! I’ve updated the condition so that the button only hides if the deactivation time is in the past.