Revert to ArchiveLoader and allow it to pass through task checks

As it's already running in production, the 'tar' visit type is now immutable. So we cannot change anything related to it. So the loader and its visit type should not have been moved at all.

So, instead of touching that loader, adapt the check utility functions to allow those checks to be bypassed for some specific cases (like the ArchiveLoader). New loaders should fix their assertion failure immediately though.

Refs. swh/infra/sysadm-environment#4906 (closed)