input: Write a python function to remove all vowels from a given string.
  assert remove_vowels("hello world") == "hll wrld"
  assert remove_vowels("AEIOUaeiou") == ""
  assert remove_vowels("Python Programming") == "Pythn Prgrmmng"
output: def remove_vowels(s: str) -> str:
      vowels = "aeiouAEIOU"
      return ''.join(char for char in s if char not in vowels)