fix: hide Hept gain until appropriate time

[Fillyosopher]

Hepteracts are using a different logic for show/hide than other cube types, which is causing them to show too early. This change uses the same css strategy used by other elements, but extends it to chal15 completions.

Reported here: https://discord.com/channels/677271830838640680/1420457591884218368/1421217317873782867

Current:

Fixed:

[Fillyosopher]

The reason there's no html change here, the hept element already has this previously non-existent css class:
https://github.com/Pseudo-Corp/SynergismOfficial/blob/master/index.html#L2622

[Pseudonian]

Apologies for the delay in responding to this PR.

It does not seem like the game uses player.challengeCompletions[15] as a marker of progress in challenge 15. Instead, we use challenge15Exponent and highestChallenge15Exponent in the player. There's also Globals.challenge15Rewards which includes a hepteractsUnlocked object.

The Challenge system is admittedly pretty messy and I should get around to redoing it at some point.

[Fillyosopher]

That makes a lot of sense. And it looks like a css class already exists for hepteract-unlock-based visibility. Pulled the changes I made, now it removes some unnecessary code and uses the existing class.

Apologies for wasting your time with the mistake!