HPCC-9762 Optimize COUNT(ITERATE(ds)) to COUNT(ds)

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4675 from ghalliday/issue9762

HPCC-9762 Optimize COUNT(ITERATE(ds)) to COUNT(ds)

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>