Move `_adjustTotalSupplyCheckpoints` inside of `createCheckpoint`

[adamdossa]

[in the dev-3.0.0 branch]

Currently we call _adjustTotalSupplyCheckpoints every time there is an operation that mints or burns tokens. However, in practice this will always be a no-op due to:

        if ((_checkpoints.length > 0) && (_checkpoints[_checkpoints.length - 1].checkpointId == _currentCheckpointId)) {
            return;
        }

in TokenLib.sol, unless a new checkpoint has been created since the last mint / burn operation.

It would be more efficient (in terms of gas consumption) to do this inside of the createCheckpoint instead.

Following the change all of the tests should still run to success, specifically c_checkpoints.js.

[dev1644]

I am working on it.

[maxsam4]

Fixed by #523