input: Write a function to delete a given key from a dictionary. If the key exists in the dictionary, remove it; otherwise, do nothing. The function should modify the dictionary in place and return nothing.
  assert delete_key({'foo': 1, 'bar': 2, 'baz': 3}, 'baz')==None
  assert delete_key({'foo': 1, 'bar': 2, 'baz': 3}, 'qux')==None
  assert delete_key({}, 'baz')==None
output: def delete_key(d, key):
      if key in d:
          del d[key]