When you try to delete a floor, an error is raised if a pos config has
an opened session. Even if the floor is not used in the opened pos
config.

The real goal of this constraint is to avoid deleting a floor plan
linked to a pos config having an opened session.

Github issue: https://github.com/odoo/odoo/issues/38581



closes odoo/odoo#38719

X-original-commit: 9ec5a4c0
Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>