Define plat_file_contexts_cts for testAospFileContexts am: 87df87e2f4

Original change: https://android-review.googlesource.com/c/platform/system/sepolicy/+/3496836

Change-Id: I33a721c21492322396083f61cec4ba1bfa598d6f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>