Remove unneeded include from test_signin_client.cc

This include causes complications when splitting
//components/signin/core/browser:test_support into "internals"
and "externals" targets: test_signin_client.h will go into the
"internals" target, which should not depend on
//components/signin/core/browser, which the included file is part of.

Happily, this include isn't used and can be removed :).

Bug: 901859
Change-Id: Ia9cd8381773801932af31856e45f9aa2a54b38c5
Reviewed-on: https://chromium-review.googlesource.com/c/1319590Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606006}

components/signin/core/browser/test_signin_client.cc

@@ -8,7 +8,6 @@
 
 #include "base/logging.h"
 #include "base/threading/thread_task_runner_handle.h"
-#include "components/signin/core/browser/webdata/token_service_table.h"
 #include "services/network/public/cpp/shared_url_loader_factory.h"
 #include "testing/gtest/include/gtest/gtest.h"