HPCC-10348 Ensure DISTRIBUTED removes grouping from the dataset

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #5712 from ghalliday/issue10348b

HPCC-10348 Ensure DISTRIBUTED removes grouping from the dataset

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>