[IMP] base: drop unused onchange_state

It calls `onchange_state()` on `res.partner` which was removed on
(24aba60).

It was added to `res.users` long ago (009ea40) to support a `state_id`
field on the view `res.users.simplified.form` that is no longer there
since v8.0.

The method is then never called and was crashing if called.

Closes #17772

odoo/addons/base/res/res_users.py

@@ -270,10 +270,6 @@ class Users(models.Model):
         if self.login and tools.single_email_re.match(self.login):
             self.email = self.login
 
-    @api.onchange('state_id')
-    def onchange_state(self):
-        return self.mapped('partner_id').onchange_state()
-
     @api.onchange('parent_id')
     def onchange_parent_id(self):
         return self.mapped('partner_id').onchange_parent_id()