Hide and make systemapi visual voicemail-related apis.

Since there are no third-party apps expected to be using the visual
voicemail related apps at the moment, best to keep these hidden for now.

Bug: 19236241
Change-Id: I86f622208efcc89fab523f03d2bb70c244cdf867
diff --git a/telecomm/java/android/telecom/AuthenticatorService.java b/telecomm/java/android/telecom/AuthenticatorService.java
index 39717c3..7aa105d 100644
--- a/telecomm/java/android/telecom/AuthenticatorService.java
+++ b/telecomm/java/android/telecom/AuthenticatorService.java
@@ -19,6 +19,7 @@
 import android.accounts.Account;
 import android.accounts.AccountAuthenticatorResponse;
 import android.accounts.NetworkErrorException;
+import android.annotation.SystemApi;
 import android.app.Service;
 import android.content.Context;
 import android.content.Intent;
@@ -28,7 +29,10 @@
 /**
  * A generic stub account authenticator service often used for sync adapters that do not directly
  * involve accounts.
+ *
+ * @hide
  */
+@SystemApi
 public class AuthenticatorService extends Service {
     private static Authenticator mAuthenticator;