Remove/delete my equestrian center

Sadly you can't delete equestrian centres anymore. We haven't been able to for years now.

The only thing to do is what you have done really, don't buy boxes or fields etc. Just don't use it.

Darn.. okay thank you.

Though, you could just use it for cattle. 6 large meadows with troughs will bring in around a million equus per month if you just harvest and sell it. You don't have to do anything to get the max amount

You can't delete an EC, but you also don't have to use it to run a boarding stable.

If you want to keep a few boxes for your own horses, you can do that.

Equally, you can have zero boxes and just use the place for a crop farm (whether cattle or plant crops). The only thing about that will be that you won't have very high prestige, which means you won't be able to use more than one workshop (with no boxes or boarders I don't know if you'd get EC prestige above 20% to allow the use of two workshops). Even so, you'll have some income from the EC which will help your game.