Hide NonNull and Nullable.

These should not be used in app code; instead, we will add
class-file retention versions of these to the support
library.

Change-Id: I13275bd28529f5da04d923688655be35c77dbb1c

api/current.txt

@@ -2676,12 +2676,6 @@ package android.animation {
 
 package android.annotation {
 
-  public abstract class NonNull implements java.lang.annotation.Annotation {
-  }
-
-  public abstract class Nullable implements java.lang.annotation.Annotation {
-  }
-
   public abstract class SuppressLint implements java.lang.annotation.Annotation {
   }
 

core/java/android/annotation/NonNull.java

@@ -27,6 +27,8 @@ import static java.lang.annotation.RetentionPolicy.SOURCE;
  * Denotes that a parameter, field or method return value can never be null.
  * <p>
  * This is a marker annotation and it has no specific attributes.
+ *
+ * @hide
  */
 @Retention(SOURCE)
 @Target({METHOD, PARAMETER, FIELD})

core/java/android/annotation/Nullable.java

@@ -34,6 +34,8 @@ import static java.lang.annotation.RetentionPolicy.SOURCE;
  * null.
  * <p>
  * This is a marker annotation and it has no specific attributes.
+ *
+ * @hide
  */
 @Retention(SOURCE)
 @Target({METHOD, PARAMETER, FIELD})