[FIX] hr_skills: Allow deleting skill, skill levels and skill types

PURPOSE
=======

Starting from 16.0 we introduced some reports to log skills history, skills evolution.

It means that the skill model is linked to another model, preventing us to delete it.

Usually, we use the message "link to x, archive it instead", but archiving a skill will only be possible from v17 (new task)

So, we need to be able to delete a skill on v16

closes odoo/odoo#131158

Taskid: 3456843
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>