HPCC-10061 Don't remove subsorts if the input has no known sort order

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-10061 Move test case into runtime regression suite

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-10061 Remove duplicated test case

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4910 from ghalliday/issue10061

HPCC-10061 Don't remove subsorts if the input has no known sort order

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>