Add maxTargetSdk restriction to unused APIs.

These are APIs that have @UnsupportedAppUsage but for which we don't
have any evidence of them currently being used, so should be safe to
remove from the unsupported list.

Bug: 170729553
Test: Treehugger
Change-Id: I4c8fd0006f950de9955242e93968fb0996ceb372

graphics/java/android/graphics/Paint.java

@@ -53,7 +53,7 @@ import java.util.Locale;
  */
 public class Paint {
 
-    @UnsupportedAppUsage
+    @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
     private long mNativePaint;
     private long mNativeShader;
     private long mNativeColorFilter;