input: Write a function to remove vowels from an alphanumeric string.
  assert remove_vowels("AaBbCc0d1e2f3g4h5i6j7k8l9m") == "BbCc0d1f3g4h5j6k7l8m9"
  assert remove_vowels("Hello123World") == "Hll123Wrld"
  assert remove_vowels("AEIOUaeiou") == ""
output: def remove_vowels(s):
      vowels = "AEIOUaeiou"
      return ''.join(char for char in s if char not in vowels)