Check that transfer_all on a linked account does not lead to empty linked account

Not sure which behavior we want to have but after #153 (closed) it would be better to simply unlink the account.

changed milestone to %runtime-801

changed milestone to %runtime-802

assigned to @bgallois

mentioned in merge request !253 (merged)

closed with merge request !253 (merged)

closed with commit 431ff35b

mentioned in commit 431ff35b

mentioned in commit b51a46dc