Fix review - simplified refund logic

[FlacoJones]

Removes the following methods from BountyCore.sol:

• getLockedFunds

• Modifies the logic of DepositManagerV1::refundDeposit to simple "refund whatever is left" with the following code:

        address depToken = bounty.tokenAddress(_depositId);
        uint256 depositVolume = bounty.volume(_depositId);
        uint256 tokenBalance = bounty.getTokenBalance(depToken);

        uint256 volume;
        if (depositVolume <= tokenBalance) {
            volume = depositVolume;
        } else {
            volume = tokenBalance;
        }

        bounty.refundDeposit(_depositId, msg.sender, volume);

[IAm0x52]

Changes look good. The refund logic has been simplified to match the newly simplified funding logic.