HPCC-8913 Remove a deprecated and unused IResultSet interface

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4057 from ghalliday/issue8913

HPCC-8913 Remove a deprecated and unused IResultSet interface

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>