Split Build: Clear tf-m-tests defualt version

Auto-parsing tf-m-tests version is also supported in tf-m-split-build
job. So clear the default setting of tf-m-tests version.

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I9d5025a0c443be45c486d41162fd79105d596812
1 file changed