Remove group description on the groups overview page

As reported by fredericnevers in MDLQA-10486:

Steps to reproduce:

1. Create a few groups with descriptions
2. Go to the groups overview page group/overview.php
3. Move your mouse over the page

Actual result:

The group description is displayed below the group name, overlapping the group listed below.

Expected result:

Having the group description displayed when mousing over the group name is unexpected behaviour. If it is necessary to display group descriptions on the group overview page (maybe it isn't?) then I would expect the table to include a column for group descriptions.

This bug may be observed on https://school.moodledemo.net/group/overview.php?id=62 if you log in as a teacher.

The  bug is the same in Clean and in Boost.