tf-m-split-build: Leave PSA_ARCH_TESTS_VERSION empty

Version of PSA arch tests can be parsed from tf-m-tests. So there is no
need to set a fixed versions value.

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I422535f806272f074b838b071c9d8e4af883c14f
1 file changed