remove now-obsolete note that engine's don't support ssh

docs/source/parallel/parallel_security.txt

@@ -105,9 +105,6 b' use OpenSSH or Paramiko, or the tunneling utilities are insufficient, then they '
 construct the tunnels themselves, and simply connect clients and engines as if the
 controller were on loopback on the connecting machine.
 
-.. note::
-
-    There is not currently tunneling available for engines.
 
 Authentication
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