Disable Feed v2 build flag on stable channel

Bug: 1129504
Change-Id: Icb74a2b914c65ba2cfda14409f0d7a7642d132f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417049
Auto-Submit: Carlos Knippschild <carlosk@chromium.org>
Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Commit-Queue: Justin DeWitt <dewittj@chromium.org>
Commit-Queue: Carlos Knippschild <carlosk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808013}

components/feed/features.gni

@@ -2,7 +2,9 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//chrome/android/channel.gni")
+
 declare_args() {
   enable_feed_in_chrome = is_android
-  enable_feed_v2 = is_android
+  enable_feed_v2 = is_android && android_channel != "stable"
 }