input: Write a python function to remove a specified element from a given string of words.
  assert remove_elem("the quick brown fox jumps over the lazy dog", "the") == "quick brown fox jumps over lazy dog"
  assert remove_elem("hello world hello", "hello") == "world"
  assert remove_elem("apple banana orange apple", "apple") == "banana orange"
output: def remove_elem(sentence, word):
      return ' '.join(w for w in sentence.split() if w != word)