"We will not use it, it needs to be repaired and we do not want a hot tub." Sounds as if you've answered your own question. Remove the thing.
Is this a wooden tub or a regular hot tub with wood for pretty?
How deep is it? Does it drain well?
Does the water system work, could you reconfigure it for irrigation purposes? You could use it for a planter as long as it has adequate drainage. I wouldn't put a tree in it, not enough room and dangerous near the house/deck.
Is the wood in contact with the soil? If so have you checked it for termites?
Pack rats? Definitely don't want those guys near the house. Make sure field mice aren't in there too, they can carry Hantavirus.

I would worry about it being too heavy, and the soil would be hard to keep aerated. Deep planters usually turn stagnant in the bottom.

I recommend removal and using any leftover redwood for smaller planters.

nmgirl: it is entirely solid wood. I'd say about 4 1/2 feet deep with a 3 1/2 foot diameter? No contact with soil beneath...the builders did a great job of making sure none of the house, entirely made of wood, contacts the soil directly. Yes, rats and mice make me nervous.

lazygardens: We can remove it and using the leftover wood for planters makes a lot of sense, I love to reuse things, because we have lots of leftover stuff and no need to buy fifty dollar planters.