Remove .avatar-container from group partial

What does this MR do and why?

It removes the .avatar-container from partial `app/views/shared/groups/_group.html.haml' because it's depreciated.

Solves #435366 (closed)

Screenshots or screen recordings

before:

after:

How to set up and validate locally

1. Ensure pipelines pass
2. Make sure the groups in /users/:username/groups look the same before/after the changes