WebUI: User-Group screen: no left arrow should remain (at least for for non-admin users) since NXP-24789

In NXP-24789, a comment can be read:

We would suggest to drop the back arrow altogether, at least for master, since we do not use this metaphor anywhere else. We could just be relying on the browser's history.

This has been implemented that way since 10.2, both for Administrators and ordinary users.

Since 9.10-HF10, in the 9.10 branch, the left arrow is still seen, and for non-administrator users, this leads ot a HTTP 404, as the non-administrator cannot access .../admin/user-group-management URL, but only .../admin/user-group-management/user/ausername

Actual Behavior when clicking the blue left arrow: HTTP 404
Expected behavior: no blue left arrow, leading to no HTTP 404 in the UI.