Remove the expat and jsoncpp to reduce the binary size.

webrtc/webrtc.gni

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build/config/arm.gni")
 import("//build/config/features.gni")
@@ skipping 60 matching lines @@
   # should be generated.
   apm_debug_dump = false
 
   # Set this to true to enable BWE test logging.
   rtc_enable_bwe_test_logging = false
 
   # Set this to disable building with support for SCTP data channels.
   rtc_enable_sctp = true
 
   # Disable these to not build components which can be externally provided.
-  rtc_build_expat = true
   rtc_build_json = true
   rtc_build_libjpeg = true
   rtc_build_libsrtp = true
   rtc_build_libvpx = true
   rtc_libvpx_build_vp9 = true
   rtc_build_libyuv = true
   rtc_build_openmax_dl = true
   rtc_build_opus = true
   rtc_build_ssl = true
   rtc_build_usrsctp = true
@@ skipping 273 matching lines @@
       configs += invoker.configs
       configs -= rtc_remove_configs
       configs -= invoker.suppressed_configs
       public_configs = [ rtc_common_inherited_config ]
       if (defined(invoker.public_configs)) {
         public_configs += invoker.public_configs
       }
     }
   }
 }