Eliminate unused include of fake_oauth2_token_service.h

Clarifies the actual usage of this class, which we will be eliminating.

TBR=msarda@chromium.org

Bug: 967598
Change-Id: I09fe4197aa8e6ae22e1f837fd21186555074971a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1678321Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672531}

components/signin/core/browser/account_tracker_service_unittest.cc

@@ -25,7 +25,6 @@
 #include "components/signin/core/browser/fake_profile_oauth2_token_service.h"
 #include "components/signin/core/browser/signin_pref_names.h"
 #include "components/signin/core/browser/test_signin_client.h"
-#include "google_apis/gaia/fake_oauth2_token_service.h"
 #include "google_apis/gaia/gaia_oauth_client.h"
 #include "google_apis/gaia/gaia_urls.h"
 #include "net/http/http_status_code.h"