drop the IBM archive endpoint from stage

[jmartin-sul]

blocked by #2418

• remove the pres cat stage shared_configs section for zip_endpoints.ibm_us_south
• pause the stage sidekiq workers and let the queues drain
• remove the relevant database records
  • in a transaction: remove the zip_parts for the ibm_us_south endpoint, then remove the zipped_moab_versions, then delete the zip_endpoint entry itself.
• give ops the all clear to remove the IBM bucket itself
• puppet: remove the secret_access_key value from the env vars that provide runtime values from vault for the setting gem