Remove old patient assignment API endpoints [MPIAPI]

[ericbuckley]

Summary

Remove the old patient assignment endpoints.

Details / Tasks

After the work in #158 has been completed, and at least one release has been created, we can move forward with deleting the old patient assignment endpoints. Remove:
POST /patient/<patient_reference_id>/person
PATCH /patient/<patient_reference_id>/person

Background / Context

This functionality now exists on the /person namespace, so we can move forward.

Dependencies

#158

Related Issues/PRs

#155

Notes / Comments

It's important to allow for at least one release to be pushed with the changes in #158 before completing this work. This gives users an opportunity to deploy a build with backwards compatibility functionality. Allowing them time to make changes in their system before these endpoints have been removed.