message: Deprecated dict `iteritems` -> `items` and remove unused imports
  Summary:
  In Python 3 `iteritems` is deprecated and replaced by `items`.
  Side note: `items` implementation differs between Python 2 and Python 3.
diff: @@ -330,7 +330,7 @@ def update_proguard_mapping_file(pg_map, redex_map, output_file):
  print(line.rstrip(), file=output)
  else:
  print(line.rstrip(), file=output)
  - for unmangled, mangled in redex_dict.iteritems():
  + for unmangled, mangled in redex_dict.items():
  print('%s -> %s:' % (unmangled, mangled), file=output)
  