Revert "Correct cylc jobfile Korn shell function definition syntax."

This reverts commit 1416b3763467670cfef70b3ce948dea8441f4610.
Correct cylc jobfile Korn shell function definition syntax.

The documentation notes that the shell command in the job submission
configuration section (i.e. the shell used to interpret the job script
submitted by cylc) allows for either Bourne shell (e.g. /bin/bash)
or a Korn shell (/bin/ksh) since they use similar styles for defining
environment variables.  However, switching this to use the Korn shell
results in a syntax error. The HANDLE_TRAP function written into
the cylc script uses Bourne shell syntax with a '()' following the
function name, which gives an error when parsed by the Korn shell.

This change modifies the function written out to the job file to use
syntax apprpriate for both shells.