Course with no groups forced should not have a groups column on the participants page

Steps to reproduce:

1. Create a course (or update an existing course) and set group mode to 'No groups' and 'Force group mode' to Yes.
2. Go to the participants page.
3. Enrol at least one user in the course.

Expected result: There should be no column for groups.

Actual result: There is a groups column with 'No groups' for each participant.