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
diff --git a/app_broker/CMakeLists.txt b/app_broker/CMakeLists.txt
index 2a8a6eb..cc6622c 100644
--- a/app_broker/CMakeLists.txt
+++ b/app_broker/CMakeLists.txt
@@ -38,9 +38,3 @@
     add_subdirectory(multi_core)
     target_link_libraries(tfm_test_broker PUBLIC ns_multi_core)
 endif()
-
-# platform_region_defs needed by PS tests
-add_library(platform_region_defs INTERFACE)
-
-
-