feedv2: revert back to app_type=2

AppType 2 is for the test application, but we're using that ID for
now. If you use 3, the server responds with no content.

Change-Id: Idf4cf0e2df21546d0a644f7502d837225d38ef2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2231580
Auto-Submit: Dan H <harringtond@chromium.org>
Reviewed-by: Ian Wells <iwells@chromium.org>
Commit-Queue: Ian Wells <iwells@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775275}

components/feed/core/proto/v2/wire/client_info.proto

@@ -21,7 +21,9 @@ message ClientInfo {
     IOS = 2;
   }
 
-  enum AppType { CLANK = 3; }
+  // TODO(harringtond): This should be CLANK = 3, but the server isn't yet
+  // updated to support it.
+  enum AppType { CLANK = 2; }
 
   // The type of OS that the client is running.
   optional PlatformType platform_type = 1;