Remove @CorePlatformApi usage in libcore/

No behavior change is expected, because the kCorePlatformApi bit of
each method / field is still set in the core-libart and core-oj dex
files. During the build of ART module, the module-lib stub is passed as
a core_platform_api stub in the "art-bootclasspath-fragment", and thus set
the kCorePlatformApi into the generated dex files.

Bug: 192446466
Test: m droid
Change-Id: Ia9371b93184c678dc42f2bff582f381d1e5f5ac2
diff --git a/ojluni/annotations/README b/ojluni/annotations/README
index 15d9738..7b5c4d4 100644
--- a/ojluni/annotations/README
+++ b/ojluni/annotations/README
@@ -33,7 +33,7 @@
    2. make openjdk-mmodule-stubs-no-javadoc
    3. FILES="your/package/and/Class.java another/package/AnotherClass.java"; for FILE in $FILES; do mkdir -p libcore/ojluni/annotations/mmodule/$(dirname ${FILE}) && unzip out/soong/.intermediates/libcore/openjdk-mmodule-stubs-no-javadoc/android_common/metalava/openjdk-mmodule-stubs-no-javadoc-stubs.srcjar ${FILE} && mv ${FILE} libcore/ojluni/annotations/mmodule/${FILE/%.java/.annotated.java}; done
    4. Add @libcore.api.Hide to each class, methods and fields in the new files. This will prevent it from being added to the public API. A JavaDoc @hide tag will not work as metalava will ignore javadoc from the stub files.
-   5. Add @libcore.api.CorePlatformApi and @libcore.api.IntraCoreApi as desired
+   5. Add @android.annotation.SystemApi(client = MODULE_LIBRARIES) and @libcore.api.IntraCoreApi as desired
       to the classes and members.
  - To see the effect of the files under this directory:
    1. make make core-platform-api-stubs core-intra-stubs