mntner with legacy auth can't be deleted

[rubenskuhl]

Describe the bug
A mntner with a method supported only for legacy authentication (like CRYPT-PW) can't be removed

To Reproduce
Have a previous object with CRYPT-PW, try deleting it.
ERROR: Invalid auth attribute: CRYPT-PW DummyValue: supported options are MD5-PW, BCRYPT-PW, PGPKEY-xxxxxxxx and IRRD-INTERNAL-AUTH for migrated objects

Expected behaviour
Deleting should care only about primary keys. The object should be removed.

IRRd version you are running
4.4.3

Additional context
This was probably introduced either by the code that enables legacy authentication in 4.4 mainline or the fix in 4.4.3

[mxsasha]

I agree this should work. This is a more specific duplicate of #647

[rubenskuhl]

I agree this should work. This is a more specific duplicate of #647

I think solving #647 would solve this one, but they are different since this was introduced alongside the concept of phasing out legacy authentication methods. So I don't know which way you prefer handling it.

Also different is that auth is a required field in mntner objects... so the workaround is different from the other fields from #647. For those, omitting the field works better; for auth, it needs to be replaced with a currently valid for new passwords auth scheme.