levm: think about logic of getting accounts and their storage

[JereSalo]

Currently when we get the storage slot of a given address and key, we not only get the storage slot from the database, but we also retrieve the account info with it.
That action warms the storage slot and also the account info. This behavior may be the wrong one.
Maybe what we have to do is just warm the storage slot but not the account info. In this case we should change the logic of our access to accounts.