HPCC-8544 Remove deprecated syntax DATASET <expression>

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #3842 from ghalliday/issue8544

HPCC-8544 Remove deprecated syntax DATASET <expression>

Reviewed-By: Richard Chapman <rchapan@hpccsystems.com>