Revert of [Android] Enable multidex for release builds of chrome_public_test_apk.

build/android/main_dex_classes.flags

-# Copyright 2017 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-# Proguard flags for what should be kept in the main dex. Only used
-# during main dex list determination, not during actual proguarding.
-
 -keep @**.MainDex class * {
   *;
 }
 
 -keepclasseswithmembers class * {
   public static ** asInterface(android.os.IBinder);
 }
 
 # Required when code coverage is enabled.
 -keep class com.vladium.** {
     *;
 }