Remove support for syncing repos with md5, sha1 checksums

[dralley]

Once EL7 has been out of support for a bit (let's call it a year and change, late 2025), support for these checksums can be dropped entirely.

At that point we could consider dropping them from Pulp entirely (that is, artifacts too).

[dralley]

Re-evaluate when that time comes

[dralley]

This goes hand-in-hand with https://github.com/pulp/pulpcore/issues/4726, if we can't do 4726 we probably wouldn't do this.