Remove unused macro ENABLE_CUSTOM_SCHEME_HANDLER

Source/build/features.gypi

 #
 # Copyright (C) 2009 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #
 
 {
   # The following defines turn WebKit features on and off.
   'variables': {
     'feature_defines': [
-      'ENABLE_CUSTOM_SCHEME_HANDLER=0',
       'ENABLE_SVG_FONTS=1',
       # WTF_USE_DYNAMIC_ANNOTATIONS=1 may be defined in build/common.gypi
       # We can't define it here because it should be present only
       # in Debug or release_valgrind_build=1 builds.
     ],
     # We have to nest variables inside variables so that they can be overridden
     # through GYP_DEFINES.
     'variables': {
       # Enables the Oilpan garbage-collection infrastructure.
       'enable_oilpan%': 0,
@@ skipping 61 matching lines @@
         ],
       }],
       ['blink_logging_always_on==1', {
         'feature_defines': [
           'LOG_DISABLED=0',
         ],
       }],
     ],
   },
 }