input: Write a function to remove all whitespace characters from each string in a given list. If the list is empty, return it as is.
  def remove_whitespace(word_list):
      return [word.replace(" ", "") for word in word_list]
  assert remove_whitespace(['Hello  World  ', 'Hi  there', 'Good  Morning'])==['HelloWorld', 'Hithere', 'GoodMorning']
  assert remove_whitespace([])==[]
output: def remove_whitespace(word_list):
      return [word.replace(" ", "") for word in word_list]