Fix build: track the naming change

package com.android.inputmethod.latin;

import android.app.backup.BackupHelperAgent;

import android.app.backup.BackupAgentHelper;

import android.app.backup.SharedPreferencesBackupHelper;

/**

 * Backs up the Latin IME shared preferences.

 */

public class LatinIMEBackupAgent extends BackupHelperAgent {

public class LatinIMEBackupAgent extends BackupAgentHelper {

    public void onCreate() {

        addHelper("shared_pref", new SharedPreferencesBackupHelper(this,