hub: remove a separate model used for a single permission

[lzaoral]

The errata_xmlrpc_scan user permission was moved to the more appropriate Scan model.

[lzaoral]

I've recreated the migration to resolve a conflict with another migration from #107.

[kdudka]

Works as expected. Thanks!

[kdudka]

@lzaoral I am not able to update user permissions through web UI for a user name that contains /:

Enter a valid username. This value may contain only letters, numbers and @/./+/-/_ characters.

In this case, the user is a Kerberos service principal. However, last week I hit a similar problem with a user named worker/..., which OSH/kobo automatically creates for each worker. Any idea if we could somehow relax this check at /osh/admin/kobo_auth/user/?

Apparently, such users exist in OSH and anything but Django Admin is able to work with them.

[lzaoral]

@lzaoral I am not able to update user permissions through web UI for a user name that contains /:

Enter a valid username. This value may contain only letters, numbers and @/./+/-/_ characters.

In this case, the user is a Kerberos service principal. However, last week I hit a similar problem with a user named worker/..., which OSH/kobo automatically creates for each worker. Any idea if we could somehow relax this check at /osh/admin/kobo_auth/user/?

Apparently, such users exist in OSH and anything but Django Admin is able to work with them.

This is an issue unrelated to this PR. Moved to #185.