[FIX] base: delete orphan translations without access right errors

Deleting an orphan translation is mostly impossible, since it requires
'write' access on the corresponding records, and checking access rights
fails because the records no longer exist!

Simply enable operations on orphan translations by ignoring the
corresponding records that do not exist.  And make sure that the patch
does not allow to create orphan translations.

closes odoo/odoo#86788

X-original-commit: cf6aed79
Signed-off-by: Raphael Collet <rco@odoo.com>
Co-authored-by: Martin Trigaux <mat@odoo.com>