The "cylc submit" command should not write a suite env file.

The *cylc submit* command currently writes a suite env file to the suite run directory, which is unnecessary because there is no running suite as far as *submit* is concerned.  If the suite is running at the same time its tasks will suddenly cease to be able to "phone home" because the suite env file will specify a port number of "None"! 

This only became a bug in cylc-5.4.5 when we made *cylc submit* use the proper suite run directory so that it can work with Rose suites (which may install files required by tasks into the suite run directory).

@matthewrmshin - please review.