cleanup dead nanomsg and build_overrides

bin/sync-and-gyp

 #!/usr/bin/env python
 
 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script will update Skia's dependencies as necessary and run
 # gyp if needed.
 
@@ skipping 59 matching lines @@
 for filename in sorted(listfiles('gyp', '*')):
   with open(filename, 'r') as f:
     hasher.update(f.read())
 
 find_dirs = [
     'bench',
     'fuzz',
     'gm',
     'tests',
     'third_party/externals/icu/source/common',
-    'third_party/externals/nanomsg/src',
     'third_party/externals/sfntly/sfntly',
     'third_party/externals/shaderc2',
     'tools/VisualBench',
     'tools/gpu',
     'tools/kilobench',
     'tools/skiaserve',
     'tools/skiaserve/urlhandlers',
     'tools/vulkan',
 ]
 
 for dir in find_dirs:
   for filename in sorted(listfiles(dir, '*.c*')):
     hasher.update(filename + '\n')
 
 gyp_hash = hasher.hexdigest()
 
 def cat_if_exists(path):
   if os.path.exists(path):
     with open(path, 'r') as f:
       return f.read()
   return ''
 
 if cat_if_exists(hash_path).strip() != gyp_hash:
   env = os.environ.copy()
   if skia_out:
     env['SKIA_OUT'] = skia_out
   subprocess.call(['python', './gyp_skia'], env=env)
   with open(hash_path, 'w') as o:
     o.write(gyp_hash)