This change removes an older workaround for tracking delegated model relationships because newer rules now require those relationships to be declared directly. It keeps Odoo's internal model information simpler and more consistent, with no expected direct impact on day-to-day users.

Since 56a666c10a74e18efa824a5797241626ac8e28fc, the declaration of `_inherits` is now required.
We can thus revert 6577920cb657a8c7f099dd05dfdd19e209de9a19, as it is not needed anymore.