input: Write a function to delete a given key from a dictionary. If the key is present in the dictionary, remove it and return None. If the key is not present, return None as well.
  
  def delete_key(dic, k):
    if k in dic:
      del dic[k]
  
  assert delete_key({'foo': 1, 'bar': 2, 'baz': 3}, 'baz') is None
  assert {'foo': 1, 'bar': 2}
  assert delete_key({'foo': 1, 'bar': 2, 'baz': 3}, 'qux') is None
  assert {'foo': 1, 'bar': 2, 'baz': 3}
  assert delete_key({}, 'foo') is None
  assert {}
output: def delete_key(dic, k):
    if k in dic:
      del dic[k]