[CLEANUP] update errata notes for 5.0 Errata

[jgh]

Summary

Update errata notes, as all of the links to the security announcements point to dead links.

Test Plan

If approved, I would like to update the notes in _all_ of the errata for past releases.

[gjb]

Please do not do this. The release notes files are generated from the base/ repository, and as of result of this, cannot be updated after the release. (This is why we have errata.html files).

Aside from that, 5.0-RELEASE is far EoL, and it would be impossible to expect all URLs from previous releases would be valid years later.

[jgh]

I understand, however it is unfortunate as I am finding all of the security bulletins, so far, in place in the new location.