Do not display records removed from Many2Many on wizard

When using a Many2Many on a wizard, the record removed have an positive id so they are not removed from the display but just greyed. But this is confusing because the removal is not deferred to the save (as there is no save). Also it is confusing for usage like in #8142 (closed).

So I think we should remove such record with positive id if the parent record has a negative id (a transient record).

The side effect will be that a new unsaved record, such record will be also removed from the display but this is still coherent as there will be no removal operation on the server side at the creation.