move ServiceState.getDataRegState to greylist

given we don't have a public alternatives for dataregstate for Q,
thus we shouldn't move this API to app-compat dark list.

Bug: 123099466
Test: Build
Change-Id: I67531ce536e004e1bc0f764824a261fb51cd27fa

telephony/java/android/telephony/ServiceState.java

@@ -540,7 +540,7 @@ public class ServiceState implements Parcelable {
      *
      * @hide
      */
-    @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
+    @UnsupportedAppUsage
     public int getDataRegState() {
         return mDataRegState;
     }