HPCC-11445 Roxie not stopping unused sink activities

Reinstate code that was removed in 3.8 when tidying up code that was believed
to be unused.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5881 from richardkchapman/reset-sinks

HPCC-11445 Roxie not stopping unused sink activities

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>