[BLOCKED] remove IBM archive endpoint related code

[jmartin-sul]

blocked by #2427, #2428, #2429

once the IBM endpoint has been dropped from all envs, we can drop the IBM related code:

• https://github.com/sul-dlss/preservation_catalog/blob/main/app/services/audit/replication_to_ibm.rb
• https://github.com/sul-dlss/preservation_catalog/blob/main/app/services/replication/ibm_provider.rb
• https://github.com/sul-dlss/preservation_catalog/blob/main/app/jobs/replication/ibm_south_delivery_job.rb
• ZipEndpoint.delivery_class enum value for Replication::IbmSouthDeliveryJob (maybe goes without saying since there's a comment, but don't change the other enum mappings!)
• related spec files
• an IBM related test setting

that might be all, but i kind of doubt it. likely worth at least a grep and a filename search for ibm (case-insensitive for both).