Drop wheel group configuration

Summary:
Debian doesn't provide a 'wheel' group, but another gid 0 group.

If we use sudo and not su, there is no incentive to use wheel group,
and as such, we can drop the extra configuration.

This change partially reverts c18cf34de2bb.

Ref T1034

Test Plan: salt-call state.apply roles/shellserver/users

Reviewers: Sandlayth

Reviewed By: Sandlayth

Maniphest Tasks: T1034

Differential Revision: https://devcentral.nasqueron.org/D1068