[FIX] core: do not mark `ir.model*` unique fields as modified

These field combinations [1] are actually secondary keys. They are
unique and represent the record identity.

Marking them as modified had a nasty side-effect: on some models, there
is a m2o to an ir.model and a stored related to ir.model/model that will
be recomputed at each model reflection. This can take some time on big
tables.
Moreover, some other stored fields may depend on those ir.model/model
related store, which adds useless time lost at recomputing unchanged
values.

[1] ir.model/model, ir.model.fields/{model,name} and
    ir.model.selection/{field_id,name}

closes odoo/odoo#54126

X-original-commit: db013a01ca4e10640ac33a59466c9cb5746e3698
Signed-off-by: Raphael Collet (rco) <rco@openerp.com>
Signed-off-by: Christophe Simonis <chs@odoo.com>