[FIX] base: deleting selection fields of non tabled models

When a model selection record is going to be deleted, a _process_ondelete method is called in order to delete all the records of the corresponding model that have that selection. These records are obtained by calling _get_records, which uses a query that needs a table. Thus, we should avoid cases for non-abstract models that have _auto = False.

closes odoo/odoo#132751

Signed-off-by: Raphael Collet <rco@odoo.com>