[recipes.py] use argparse to set command automatically.

recipe_engine/refs.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 from __future__ import print_function
 
 from . import loader
 
 
 def add_subparser(parser):
   helpstr = 'List places referencing given recipe module(s).'
   refs_p = parser.add_parser(
       'refs', help=helpstr, description=helpstr)
   refs_p.add_argument('modules', nargs='+', help='Module(s) to query for')
   refs_p.add_argument('--transitive', action='store_true',
                       help='Compute transitive closure of the references')
 
-  refs_p.set_defaults(command='refs', func=main)
+  refs_p.set_defaults(func=main)
 
 
 def main(package_deps, args):
   universe = loader.RecipeUniverse(package_deps, args.package)
   own_package = package_deps.root_package
   modules = args.modules
   transitive = args.transitive
 
   result_modules = set()
   result_recipes = set()
@@ skipping 30 matching lines @@
 
   if result_modules:
     print('Modules:')
     for module in sorted(result_modules):
       print('  %s' % module)
 
   if result_recipes:
     print('Recipes:')
     for recipe in sorted(result_recipes):
       print('  %s' % recipe)