[FIX]util/models: improve query for custom fields

[npm-odoo]

When utilizing 'def remove_inherit_from_model' method, it removes fields to disconnect two models, eliminating all custom fields created by customers. To prevent this, adding one condition.

Recentally i saw that issue here Here he tries to remove the connection between base.automation and ir.act.server. If customers have created custom fields using the studio in the base.automation model, this method will remove all custom fields during migration.