Make MediaStore.Audio.Radio not instantiable

Types which only contain constants or static methods should
not be instantiable.

Bug: 15430601
Change-Id: I515740e677ae4c72afc09e943e20a72ea27cb17e

api/current.txt

@@ -24264,7 +24264,6 @@ package android.provider {
   }
 
   public static final class MediaStore.Audio.Radio {
-    ctor public MediaStore.Audio.Radio();
     field public static final java.lang.String ENTRY_CONTENT_TYPE = "vnd.android.cursor.item/radio";
   }
 

core/java/android/provider/MediaStore.java

@@ -1886,6 +1886,9 @@ public final class MediaStore {
              * The MIME type for entries in this table.
              */
             public static final String ENTRY_CONTENT_TYPE = "vnd.android.cursor.item/radio";
+
+            // Not instantiable.
+            private Radio() { }
         }
     }