HPCC-10137 Remove obsolete persist-handling methods from IGlobalCodeContext

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5443 from richardkchapman/persist-method-cleanup

HPCC-10137 Remove obsolete persist-handling methods from IGlobalCodeCont...

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>