Revert of Allow overriding GN build flags

build_overrides/pdfium.gni

Index: build_overrides/pdfium.gni
diff --git a/build_overrides/pdfium.gni b/build_overrides/pdfium.gni
deleted file mode 100644
index d032aa12a44ef58547ad1cdeb87ef136d70467a5..0000000000000000000000000000000000000000
--- a/build_overrides/pdfium.gni
+++ /dev/null
@@ -1,23 +0,0 @@
-# Copyright 2016 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-# This file contains PDFium-related build flags.
-
-declare_args() {
-  # On Android there's no system FreeType. On Windows and Mac, only a few
-  # methods are used from it.
-  pdfium_bundle_freetype = !is_linux
-
-  # Build PDFium either with or without v8 support.
-  pdf_enable_v8 = true
-
-  # Build PDFium either with or without XFA Forms support.
-  pdf_enable_xfa = false
-
-  # Build PDFium against skia (experimental) rather than agg.
-  pdf_use_skia = false
-
-  # Build PDFium standalone
-  pdf_is_standalone = false
-}