input: Write a python function to remove vowels from a given word.
  assert remove_vowels("This is a sentence") == "Ths s  sntnc"
  assert remove_vowels("Hello World") == "Hll Wrld"
  assert remove_vowels("AEIOUaeiou") == ""
output: def remove_vowels(word):
      vowels = "aeiouAEIOU"
      return "".join(char for char in word if char not in vowels)