Remove unused macro ENABLE_CUSTOM_SCHEME_HANDLER

Source/config.gni

 # Copyright 2014 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.
 
 import("//build/config/ui.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
 } else {
   # TODO(brettw) remove this once && early-out is checked in.
@@ skipping 33 matching lines @@
 use_webaudio_ffmpeg = !is_mac && !is_android
 
 # Set this to true to enable use of concatenated impulse responses for the HRTF
 # panner in WebAudio.
 # TODO(brettw) do we need this or can we assume its always on?
 use_concatenated_impulse_responses = true
 
 # feature_defines_list ---------------------------------------------------------
 
 feature_defines_list = [
-  "ENABLE_CUSTOM_SCHEME_HANDLER=0",
   "ENABLE_SVG_FONTS=1",
 ]
 
 if (is_debug) {
   # TODO(GYP) this should also be set when release_valgrind_build is set,
   # but we don't have that flag in the GN build yet.
   feature_defines_list += [ "WTF_USE_DYNAMIC_ANNOTATIONS=1" ]
 }
 
 if (use_concatenated_impulse_responses) {
@@ skipping 36 matching lines @@
 }
 
 # feature_defines_string -------------------------------------------------------
 
 # Convert the list to a space-separated string for passing to scripts.
 # This would be the equivalent of passing '<(feature_defines)' in GYP.
 feature_defines_string = exec_script(
     "build/gn_list_to_space_separated_string.py",
     feature_defines_list,
     "trim string")