R=joransiu@ca.ibm.com

Drive-by: clean up the macro on s390x since it's not used.
Change-Id: I317508c1f8a1520ee8873b4323cacd63b8a7cce2
Reviewed-on: https://chromium-review.googlesource.com/c/1398121Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#58599}