Rename PrivateApi annotation to SystemApi.

Change-Id: I97b473884f81ad375d0733e4766afe091dfdd854
diff --git a/Android.mk b/Android.mk
index 573f46a..a5746e4 100644
--- a/Android.mk
+++ b/Android.mk
@@ -718,7 +718,7 @@
 LOCAL_DROIDDOC_OPTIONS:=\
 		$(framework_docs_LOCAL_DROIDDOC_OPTIONS) \
 		-stubs $(TARGET_OUT_COMMON_INTERMEDIATES)/JAVA_LIBRARIES/android_private_stubs_current_intermediates/src \
-        -showAnnotation android.annotation.PrivateApi \
+        -showAnnotation android.annotation.SystemApi \
 		-nodocs
 
 LOCAL_DROIDDOC_CUSTOM_TEMPLATE_DIR:=build/tools/droiddoc/templates-sdk