[BUG] User Retains Manager Access to Collection After Role Revocation

[abankhele]

Describe the bug
A user with a manager role, assigned as a manager for a specific collection, retains access to the "Manage Content" section and the collection even after their manager role is revoked from the system.

To Reproduce

1. Steps to reproduce the behavior, including the results:
2. Go to 'https://avalon-staging.dlib.indiana.edu/'
3. Click on Manage Content and select a collection (e.g., Regression Testing 11/15 - editing).
4. Under Assign Staff Roles, add a user with the manager role to the Manager field.
5. Log in as the assigned user and confirm they can access the collection via Manage Content.
6. As an admin, go to the Manage dropdown and click Manage Groups.
7. Select the Manager group under System Groups.
8. Remove the user from the Manager group.
9. Log in again as the user and observe that they still have access to Manage Content and the collection.

Expected behavior
Once a user is removed from the Manager group, they should no longer see the Manage button in the navbar, nor should they have access to Manage Content or the collection.

Screenshots/Screen Recording

Environment (please complete the following information):

• Device / platform : desktop
• OS: macos
• Browser [home, safari]
• avalon-dev
• avalon-staging
• mco-staging
• mco-production
• demo

Done Looks Like

• When a user is removed from the Managers group, they are removed from the staff role listing for each collection on which they are Manager (not demoted to Editor, as was the previous behavior)
  • Removing the user from collections after this action can be sent to a background job
• If a user is removed from the Managers group but they are the sole manager on a collection, the application returns a message to the user indicating that they cannot be removed because of this