HPCC-9602 Avoid temporary variables when returing simple expressions

The "very temporary" fix has been in there for many many years, and has
been redundant for most of them.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4597 from ghalliday/issue9602

HPCC-9602 Avoid temporary variables when returing simple expressions

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>