Clean up keys from former employees

Without this patch there are former employees who still have access to
our systems.  This is a problem because they no longer work at the
company and should no longer be able to SSH into our systems.

This patch addresses the problem by cleaning up these keys.

Former employees affected are:

 * Nan Liu
 * James Turnbull
 * Dan Bode
 * Garrett Honeycutt
 * Josh Lifton
Merge branch 'cleanup'

* cleanup:
  Clean up keys from former employees