[IMP] password_security: use ir.config_parameter

[alexis-via]

Replace fields on res.company by ir.config_parameter.
Remove dead test for v16 migration script.

There is one problem with this implementation: in odoo, when you set an integer ir.config_parameter to 0, the ir.config_parameter is deleted... so Odoo will use the default value. If the default value is 0 like auth_password_policy.minlength in the module auth_password_policy of the official addons, it's OK. But, in the module password_security, the default value is NOT 0.

I propose the following:

• we set the default value to 0 in the ir.config_parameter definied in password_security
• in post-migration script, we create the ir.config_parameter with the value we want as default value

If you agree with my proposal, I'll implement it in this PR.

[alexis-via]

This PR aims at updating the v17 OCA migration PR OCA#610

[alexis-via]

I implemented what I proposed in my comment.
As this PR didn't receive any attention from DynAppsNV, I'll propose it directly to OCA