input: Write a python function to remove a specified word from a given sentence.
  assert remove_word("He is working on it", "working") == "He is  on it"
  assert remove_word("The quick brown fox jumps over the lazy dog", "quick") == "The  brown fox jumps over the lazy dog"
  assert remove_word("Hello world", "world") == "Hello "
output: def remove_word(sentence, word):
      return sentence.replace(word, '')