How do I get rid of iCloud Keychain?

What do you mean, "Get rid of"?

You can just delete passwords. It's a bit laborious, but in Passwords settings, you can find and delete passwords and they will be deleted on all devices.

Or, you can disable iCloud Keychain. Settings > Your profile > iCloud > iCloud Keychain > off (assuming iPadOS 15 still). You'll be asked if you want to keep or delete data. Now you are no longer syncing your keychain to iCloud on this device, it's all local. If you deleted data, it's still in the cloud and protected by your password, but you aren't using it. When you turn on Keychain again, whatever you have will be merged with your iCloud keychain. If you deleted data and no other devices have it, the data is lost, which means the next time you turn it on again you'll have a clear iCloud Keychain, except for any items on your device.

But if you want to delete your iCloud keychain entirely and make sure it cannot come back from any device, that's rather harder. You have to (I'm not making this up, sorry) simultaneously sign out of iCloud and then erase and reset all of your devices at once, and then, when you set up your first device, forget all your passcodes for all your other devices, until you're finally offered the chance to reset and start your keychain from scratch. I wish there were an easier way, but there isn't. It's a wee bit easier on Mac because you can just delete your keychain files, but on iOS there's simply no option to clear your keychain unconditionally from all devices at once. Needless to say this is drastic, so unless you have a good reason for doing that, I'd just disable iCloud Keychain and delete.

Be aware that certain features require iCloud Keychain to work. This infrastructure is used for end-to-end encryption and that's used by several iOS features.