Removing extraneous header include

TBR=michaelpg@chromium.org
Bug=876971

Change-Id: Ibb98fa46406252e5827b900771f65a9dd12cc27a
Reviewed-on: https://chromium-review.googlesource.com/c/1293755Reviewed-by: Joe Downing <joedow@chromium.org>
Commit-Queue: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601589}

chrome/browser/chromeos/login/demo_mode/demo_setup_browsertest.cc

@@ -14,7 +14,6 @@
 #include "base/time/time_to_iso8601.h"
 #include "base/timer/timer.h"
 #include "base/values.h"
-#include "build/build_config.h"
 #include "chrome/browser/chromeos/login/demo_mode/demo_session.h"
 #include "chrome/browser/chromeos/login/demo_mode/demo_setup_test_utils.h"
 #include "chrome/browser/chromeos/login/login_manager_test.h"