chromeos: Remove chromeos/chromeos_buildflags.

The file was migrated into build/chromeos_buildflags,
so no longer needed.

BUG=1114198
TEST=Build locally.

Change-Id: Iffafe7c3d4f2417cfbe4c1ceff21397937cbd9d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2397975Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806037}

chromeos/BUILD.gn

@@ -24,11 +24,6 @@ declare_args() {
   is_printing_ppd_provider_v3 = false
 }
 
-buildflag_header("chromeos_buildflags") {
-  header = "chromeos_buildflags.h"
-  flags = [ "IS_CHROMEOS_DEVICE=$is_chromeos_device" ]
-}
-
 component("chromeos") {
   configs += [
     ":chromeos_implementation",
@@ -161,7 +156,6 @@ test("chromeos_unittests") {
   ]
 
   deps = [
-    ":chromeos_buildflags",
     ":test_support",
     "//base/test:test_support",
     "//build:chromeos_buildflags",