Manual:$wgGroupsRemoveFromSelf

Details
$wgGroupsRemoveFromSelf allow users to remove themselves userights without the need to request it from a bureaucrat or steward. The syntax is.

Changes in 1.14.0
In r39368, the way this variable works was changed. Before, it allowed every user to remove those groups from themselves, now it can be filtered on a per-group basis.

The new syntax is  which allows any user in the group "group1" to remove the groups "group2" and "group3" from themselves. The old syntax will still work for allowing every user to remove groups from themselves, but it is recommended that you use  instead.

You may use  to allow users in that group to remove every group from themselves.