input: Write a python function to delete a key from a dictionary.
  assert delete_key({'foo': 1, 'bar': 2, 'baz': 3}, 'baz') == {'foo': 1, 'bar': 2}
  assert delete_key({'a': 10, 'b': 20, 'c': 30}, 'b') == {'a': 10, 'c': 30}
  assert delete_key({'x': 100, 'y': 200}, 'z') == {'x': 100, 'y': 200}
output: def delete_key(d, key):
      if key in d:
          del d[key]
      return d