HPCC-8991 STEPPED is supported by thor so remove the error

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4148 from ghalliday/issue8991

HPCC-8991 STEPPED is supported by thor so remove the error

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>