Use the normal suite run directory for "cylc submit" tasks.

Tasks executed sans suite via ```cylc submit``` currently use a non-standard suite run directory (namely the standard location with '-submit' appended.  This was meant to avoid contaminating the suite log directory, but it can break ```cylc submit```'ed tasks belonging to Rose-style suites that self-deploy into their own run directory (because the '-submit' run directory does not have the deployed files). This small change just removes the special treatment, and notes in the submit command help that the log location will now be the same as for suite-submitted tasks.

(wait on test for ```cylc subm``` before merge...)