HPCC-8774 Always defined type_t as an enum

This isn't stored in any persistent form, so changing the type
doesn't have any effects.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #3946 from ghalliday/issue8774

HPCC-8774 Always defined type_t as an enum

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>