Remove deprecated tools/README instructions

Remove instructions for:

experimental_ssh_eventlet.py: deleted May 25, 2014 commit 318669f

openstack: deleted Sep 30, 2013 commit f4a9c0f

heat-keystone-setup: was never in the tools directory, but has
documentation in the man pages

Change-Id: I8ae3050e16163699849342e81d302942e763ac0c
Partial-Bug: 1338066