Left-over from ipfs-log refactoring

[thiagodelgado111]

There's some leftover using the old write set as before inside the sync function (https://github.com/orbitdb/orbit-db-store/blob/master/src/Store.js#L235), that breaks when an access controller is passed to the store

[RichardLitt]

Thanks, @thiagodelgado111 :)