Fix The Great Henge cost reduction

[Susucre]

The cost reduction was not correct if the player casting the spell was not The Great Henge's owner.

For instance with cards like Gonti, Lord of Luxury or Hostage Taker, it might not be the owner's that is casting it. In such case, the cost reduction was incorrect.

[github-actions]

The Great Henge - (Gatherer) (Scryfall) (EDHREC)

{7}{G}{G}
Legendary Artifact
This spell costs {X} less to cast, where X is the greatest power among creatures you control.
{T}: Add {G}{G}. You gain 2 life.
Whenever a nontoken creature enters the battlefield under your control, put a +1/+1 counter on it and draw a card.

Gonti, Lord of Luxury - (Gatherer) (Scryfall) (EDHREC)

{2}{B}{B}
Legendary Creature — Aetherborn Rogue
2/3
Deathtouch
When Gonti, Lord of Luxury enters the battlefield, look at the top four cards of target opponent's library, exile one of them face down, then put the rest on the bottom of that library in a random order. You may cast that card for as long as it remains exiled, and mana of any type can be spent to cast it.

Hostage Taker - (Gatherer) (Scryfall) (EDHREC)

{2}{U}{B}
Creature — Human Pirate
2/3
When Hostage Taker enters the battlefield, exile another target creature or artifact until Hostage Taker leaves the battlefield. You may cast that card for as long as it remains exiled, and mana of any type can be spent to cast it.

[Susucre]

Well there might be more cards with the same issue. I'll refactor some of them in a common effect.

[Susucre]

Ok, this fix only Great Henge and can be merged, but there is almost no cost reduction / cost increase / permission that is working right when it does count/check something for the controller.
I'll make an issue for some of the bugged ones.