Temporarily disable building feedv2

Feedv2 was enabled in June, and now Pinpoint is having merge conflicts
when rebasing new patches onto pre-Elements base commits. The purpose
of this CL is to provide a more recent no-Elements base commit for perf
testing.

I will revert this change as soon as it lands.

Change-Id: I901ce90cd244a28d3213f377e9348c323cad9089
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2453804
Commit-Queue: Ian Wells <iwells@chromium.org>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814505}

components/feed/features.gni

@@ -14,7 +14,7 @@ declare_args() {
   enable_feed_v1 = is_android
 
   # Whether version 2 of the NTP feed is enabled in the build.
-  enable_feed_v2 = is_android
+  enable_feed_v2 = false
 }
 
 if (is_android && android_channel != "default") {