refactor(check)!: remove check

[k-yang]

(Highly opinionated change)

The check API and withdraw_creation_fee variables are confusing and causes an accounting error with campaign pools.

The flow of a campaign goes like this

1. deposit
2. reward_all
3. check if necessary

In deposit, an amount for the campaign is specified, and in reward_all, the amount is deducted from the campaign and added to the user pool. Contradictorily, check puts the amount back to the campaign and causes accounting errors.

For example, imagine I create a campaign nibiru-itn-rewards with 1000unibi and reward 1000unibi to address nibi1gc6vpl9j0ty8tkt53787zps9ezc70kj88hluw4. The reward_all function subtracts 1000unibi from the campaign nibiru-itn-rewards and allocates it to nibi1gc6vpl9j0ty8tkt53787zps9ezc70kj88hluw4. Note that the campaign's amount is zero now.

If I call check with campaign id nibiru-itn-rewards and with amount 1000unibi, it resets the campaign amount to 1000unibi, which breaks accounting because now I can reward another 1000unibi to another user even though the total amount of unibi in the contract hasn't changed.

In reality, if I wanted to withdraw any surplus from the campaign, I could just cancel the campaign and use the withdraw function. The existence of this alternate route means that check and withdraw_creation_fee are unnecessary and cause additional headaches. Removing them simplifies the contract and reduces the size of the state, which gives us some gas improvements.

BREAKING CHANGE: Removes check and withdraw_creation_fee.