Y25-709 - Remove obsolete accessioning code

[StephenHulme]

Describe the Housekeeping
Remove sample accessioning code in models with a particular focus on the Accessionable::Sample class that has been replaced with Accession::Sample (apologies for the similar naming...).

This includes, but is not limited to:

• Accessionable::Sample
• submit_sample_for_user
  • and everything related to the y25_286_accession_individual_samples_with_sample_accessioning_job feature flag
• Validation that no longer applies (careful here, err on the conservative side)
• References to contact_user along with the configatron.accession_local_key and it's implementation in Deployment project (see Y25-285 - Accessioning - Change the submission user to a PSD account #4878)
• FakeAccessionService - replace with an instance of one of the other AccessionServices or use the AccessioningV1Client

Blocking issues

#5414 ✅
#5415 ✅
#5416 ✅

Additional context
Add any other context about the problem here.