Removes git pre-req
Removes git pre-req

* Despite installing openshift multiple times, git has never been a
  requirement
* This would be a requirement for the development side, but not for
  installing a cluster.
* Therefore, I think it should be removed
* closes openshift/openshift-docs#3133

xiaoping378/openshift-docs,xiaoping378/openshift-docs,xiaoping378/openshift-docs