fix: remove unused code

[nolanlawson]

Jest 27 was complaining about this code path never getting hit. From looking at the code, it seems indeed impossible for the else to ever get hit - the ready() function always ensures that this._db is set, and we await it. So it will definitely always return true.

Also this should only really matter if someone calls db.close() twice or db.delete() twice... which the tests already cover.