PURPOSE
Improve performance in often used views and fields in a normal Odoo usage.
SPECIFICATIONS
On crm.lead model
* remove field user_email and user_login fields. Those are related non stored
and used in kanban for no reason (or even not used). Those can be removed
completely;
Original commit seems to be odoo/odoo@ea2e8b64c4 which seems to show those
fields were added to add a gravtar based on user email, and its login was used
to display "responsible". Maybe an internal Odoo related spec, anyway not used
anymore.
Task-2752043
Part-of: odoo/odoo#83806