Revert "Send variation headers to sync server"

This reverts commit c305a2ba.

Reason for revert: DCHECK failures observed on ios.

Original change's description:
> Send variation headers to sync server
> 
> This information is already sent to other servers such as the one used
> for omnibox personalization, hence the patch doesn't upload additional
> information but allows measuring the impact variations have on the sync
> server and debug errors caused by client-side experiments.
> 
> Bug: 887521
> Change-Id: I3358956639bf96260bb5010279012195086eec37
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1827368
> Reviewed-by: Mark Pearson <mpearson@chromium.org>
> Reviewed-by: Marc Treib <treib@chromium.org>
> Commit-Queue: Mikel Astiz <mastiz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#700678}

TBR=mpearson@chromium.org,treib@chromium.org,mastiz@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 887521, 1011088
Change-Id: I07fb576d156cf9efd334ce89617e9a823db61662
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1844814Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703254}

components/sync/BUILD.gn

@@ -430,7 +430,6 @@ jumbo_static_library("rest_of_sync") {
     "//base:i18n",
     "//build:branding_buildflags",
     "//components/keyed_service/core",
-    "//components/variations/net",
     "//services/network/public/cpp",
     "//sql",
     "//third_party/cacheinvalidation",

components/sync/engine/net/DEPS

 include_rules = [
-  "+components/variations",
   "+net",
   "+services/network/public/cpp",
   "+services/network/test",

components/sync/engine/net/http_bridge.cc

@@ -19,7 +19,6 @@
 #include "base/strings/stringprintf.h"
 #include "base/task/post_task.h"
 #include "components/sync/base/cancelation_signal.h"
-#include "components/variations/net/variations_http_headers.h"
 #include "net/base/load_flags.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_cache.h"
@@ -278,10 +277,6 @@ void HttpBridge::MakeAsynchronousPost() {
   resource_request->headers.SetHeader(net::HttpRequestHeaders::kUserAgent,
                                       user_agent_);
 
-  variations::AppendVariationsHeader(
-      url_for_request_, variations::InIncognito::kNo,
-      variations::SignedIn::kYes, resource_request.get());
-
   fetch_state_.url_loader = network::SimpleURLLoader::Create(
       std::move(resource_request), traffic_annotation);
   network::SimpleURLLoader* url_loader = fetch_state_.url_loader.get();