revert GitLab update instructions incomplete
Created by: bbodenmiller
Following https://github.com/gitlabhq/gitlabhq/blob/master/doc/update/6.x-or-7.x-to-7.3.md#things-went-south-revert-to-previous-version-60 or https://github.com/gitlabhq/gitlabhq/blob/master/doc/update/7.2-to-7.3.md#things-went-south-revert-to-previous-version-72 won't work as there is no revert instructions for the changes made on Redis to use sockets.