Use APK CtsShim prebuilts for flattened apex.

Fix: 158036322
Test: built flame-userdebug with m OVERRIDE_TARGET_FLATTEN_APEX=true, ran
atest CtsAppSecurityHostTestCases:android.appsecurity.cts.PrivilegedUpdateTests#testDisableUpdatedSystemApp
and verified that the cts shim apex is not installed

Change-Id: Icc52500cfc0a555e11d1a467b2da0649c7f5d31f

target/product/base_system.mk

@@ -51,7 +51,6 @@ PRODUCT_PACKAGES += \
     charger \
     cmd \
     com.android.adbd \
-    com.android.apex.cts.shim.v1 \
     com.android.appsearch \
     com.android.conscrypt \
     com.android.cronet \
@@ -72,6 +71,8 @@ PRODUCT_PACKAGES += \
     com.android.wifi \
     ContactsProvider \
     content \
+    CtsShimPrebuilt \
+    CtsShimPrivPrebuilt \
     debuggerd\
     device_config \
     dmctl \

target/product/updatable_apex.mk

@@ -17,6 +17,8 @@
 # Inherit this when the target needs to support updating APEXes
 
 ifneq ($(OVERRIDE_TARGET_FLATTEN_APEX),true)
+  # com.android.apex.cts.shim.v1_prebuilt overrides CtsShimPrebuilt
+  # and CtsShimPrivPrebuilt since they are packaged inside the APEX.
   PRODUCT_PACKAGES += com.android.apex.cts.shim.v1_prebuilt
   PRODUCT_PROPERTY_OVERRIDES := ro.apex.updatable=true
   TARGET_FLATTEN_APEX := false