[caissedepargne] Remove accounts with no balance

Some accounts on Caisse d'Epargne (Yoga, Tendances...) have no balance,
I checked on the website but the account details does not contain any
balance either. These accounts cause bugs in the backend so we must
remove them from self.accounts before returning the accounts list.
Same for accounts that have no label at all.

Closes: 6611@zendesk