Fix network_for_ssh config option help

The help for the network_for_ssh option says it's not used
if run_validation=False, but that's not true in the case of
scenario tests, so remove that part of the help.

Change-Id: I938afb1589ed4bb56504258e7fa285b19f772a16
diff --git a/tempest/config.py b/tempest/config.py
index ea3ed5a..251e264 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -652,7 +652,7 @@
     cfg.StrOpt('network_for_ssh',
                default='public',
                help="Network used for SSH connections. Ignored if "
-                    "connect_method=floating or run_validation=false.",
+                    "connect_method=floating.",
                deprecated_opts=[cfg.DeprecatedOpt('network_for_ssh',
                                                   group='compute')]),
 ]