Simplify Assessment deletion permission checks

[martha]

Description

Summary of changes:

• Replace the frontend logic for determining whether to show the Delete Assessment button, with one permission check that relies on the backend policy.
• Note that this is a logical change from before!
  • Previously: The backend required only can_delete_enrollments to delete a completed Intake, but the frontend required can_delete_enrollments AND can_delete_assessments.
  • After this PR: Frontend is aligned with backend on the less strict version. You only need can_delete_enrollments to delete a completed Intake.

Depends on hmis-warehouse PR: greenriver/hmis-warehouse#6505

How to test: See QA instructions on ticket

Type of change

Code clean-up

Checklist before requesting review

• I have performed a self-review of my code
• I have run the code that is being changed under ideal conditions, and it doesn't fail
• I have used Axe DevTools to scan for accessibility issues (or not applicable)
• My code includes comments and/or descriptive variable names to help other engineers understand the intent (or not applicable)
• I have updated the documentation (or not applicable)
• If it's not obvious how to test this change, I have provided testing instructions in this PR or the related issue

[gigxz]

phew good cleanup, thanks!