Took some unnecessary verbosity out of 'cylc help'.

The descriptions of pyro communication, suite passphrases, and ssh
messaging, belong in the User Guide, not top level command help.
This commit also tidies the corresponding sections of the user guide.
Removed a remnant of original batched job submission implementation.
Merge pull request #242 from hjoliver/command-help-tidy

Took some unnecessary verbosity out of 'cylc help'.