input: Write a function to delete a given key from a dictionary. If the key is not present in the dictionary, the function should do nothing. The function should return None.
  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
  assert delete_key({'foo': 1, 'bar': 2, 'baz': 3}, 'foo') == None
output: def delete_key(d, key):
      if key in d:
          del d[key]