Remove unused header from app_view_apitest.cc

This CL is a refactor with no intended behavior change.

Change-Id: Idc37eba5389894123cee25c1cabb1119e63a8bf3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2600238
Auto-Submit: Erik Chen <erikchen@chromium.org>
Commit-Queue: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Lucas Gadani <lfg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840188}

extensions/browser/guest_view/app_view/app_view_apitest.cc

@@ -6,7 +6,6 @@
 #include "base/path_service.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_restrictions.h"
-#include "build/chromeos_buildflags.h"
 #include "components/guest_view/browser/guest_view_manager.h"
 #include "components/guest_view/browser/guest_view_manager_factory.h"
 #include "components/guest_view/browser/test_guest_view_manager.h"