gtx: Remove pointless assignments from gtxtest

Remove assignments to 'code' when we're not going to pay attention
to them.

Caught by clang-analyzer

Change-Id: Ib2f8c20c0bc741d0bb1b8ed4fdb46ea61511fc95
Reviewed-on: http://gerrit.openafs.org/9204
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>