HPCC-12732 Remove unneeded '#include <malloc.h>'

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6757 from ghalliday/issue12732

HPCC-12732 Remove unneeded '#include <malloc.h>'

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>