Remove unused function in presubmit script

PRESUBMIT.py

 # Copyright 2012 the V8 project authors. 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
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 215 matching lines @@
       _CheckNoProductionCodeUsingTestOnlyFunctions(input_api, output_api))
   results.extend(
       _CheckNoInlineHeaderIncludesInNormalHeaders(input_api, output_api))
   return results
 
 
 def _SkipTreeCheck(input_api, output_api):
   """Check the env var whether we want to skip tree check.
      Only skip if include/v8-version.h has been updated."""
   src_version = 'include/v8-version.h'
-  FilterFile = lambda file: file.LocalPath() == src_version
   if not input_api.AffectedSourceFiles(
       lambda file: file.LocalPath() == src_version):
     return False
   return input_api.environ.get('PRESUBMIT_TREE_CHECK') == 'skip'
 
 
 def _CheckChangeLogFlag(input_api, output_api, warn):
   """Checks usage of LOG= flag in the commit message."""
   results = []
   if (input_api.change.BUG and input_api.change.BUG != 'none' and
@@ skipping 44 matching lines @@
       'v8_win64_rel': set(['defaulttests']),
       'v8_mac_rel': set(['defaulttests']),
       'v8_linux_arm_rel': set(['defaulttests']),
       'v8_linux_arm64_rel': set(['defaulttests']),
       'v8_linux_mipsel_compile_rel': set(['defaulttests']),
       'v8_linux_mips64el_compile_rel': set(['defaulttests']),
       'v8_android_arm_compile_rel': set(['defaulttests']),
       'v8_linux_chromium_gn_rel': set(['defaulttests']),
     },
   }