input: Write a function to remove a key-value pair from a dictionary.
  assert remove_pair({'a': 10, 'b': 20, 'c': 30}, 'c') == {'a': 10, 'b': 20}
  assert remove_pair({'a': 10, 'b': 20, 'c': 30}, 'a') == {'b': 20, 'c': 30}
  assert remove_pair({'a': 10, 'b': 20, 'c': 30}, 'd') == {'a': 10, 'b': 20, 'c': 30}
output: def remove_pair(d, key):
      if key in d:
          del d[key]
      return d