Build: Remove creation of platform_region_defs

NS platform_region_defs is defined and configured in NS CMake file
exported by TF-M in commit 6c9448.
Remove creation of platform_region_defs from tf-m-tests.

Signed-off-by: David Hu <david.hu@arm.com>
Change-Id: I67d25ed6fd7ab0f7939ecbd723216cf2823b901d
1 file changed