[FIX] account: remove bank accounts when switching move type

When switching a invoice to a refund, the bank account to which the move
should be paid should be removed: while it (might) contain the partner's
bank account before, when becoming a refund it makes no sense to keep
the partner's bank account as the recipient.

closes odoo/odoo#43085

Signed-off-by: Damien Bouvy (dbo) <dbo@odoo.com>