This PR is in preparation for the www.usability.gov and accessibility.digital.gov redirects.
[X] It updates the ACME Challenge records for usability.gov, www.usability.gov, and accessibility.digital.gov based on the current external domain service provided by cloud.gov.
[X] It removes the defunct demo.accessibility.digital.gov DNS records
[X] It temporarily removes the A records for accessibility.digital.gov and www.usability.gov in order to update them to CNAME records in a follow up PR.
This PR is in preparation for the www.usability.gov and accessibility.digital.gov redirects.