Remove MetaData→Revision foreign key

Back when IIIF imports were supposed to include Git revisions everywhere and show history, a foreign key between MetaData and Revision was created, to allow telling which commit changed a TEI file. With the new IIIF import ignoring all of Git, the deletion of Event, and the "hiding" of the TEI import in a arkindex.himanis we all choose to forget about, this link no longer has a use and adds extra unneeded SQL queries.

Approximatively 1% of all metadatas both in preprod and in prod have a revision from the previous IIIF import:

• Preprod
  • HOME | HIMANIS: 1626
  • HORAE: 5162
  • HORPIC: 82
• Prod
  • Himanis | A2iA UPV: 26209
  • Himanis | READ: 18
  • HOME | Monasterium: 87344
  • HORAE: 5291
  • HORAE | 790: 6285
  • HORPIC: 84
  • TO_DELETE Edkolscholia: 10