input: Write a python function to delete a key from a dictionary and handle the case where the key is not found.
  assert delete_key({'a': 1, 'b': 2, 'c': 3}, 'b') == {'a': 1, 'c': 3}
  assert delete_key({'x': 10, 'y': 20, 'z': 30}, 'y') == {'x': 10, 'z': 30}
  assert delete_key({'name': 'Alice', 'age': 25}, 'height') == 'Error! Key not found'
output: def delete_key(d, key):
      if key in d:
          del d[key]
          return d
      else:
          return 'Error! Key not found'