HPCC-8833 Assume keyed join is sorted unless UNORDERED

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Is this really needed? If people want unordered keyed joins they have the unordered keyword. Providing the ability to set that globally (well, for thor - Roxie generation ignores this option) seems a little unnecessary.