ARGO-294: remove depositors field from register/update APO form, as it turns out the dor-apo-depositors role doesn't do what's needed.  may return after further design.  left refactoring and unit test enhancements from earlier implementation.
Merge branch 'develop' of https://github.com/sul-dlss/argo into develop

had to edit erroneous jira issue number in prior commit