input: Write a Python function that accepts a string and outputs the string with all vowels removed.  
  assert remove_vowels('') == ''  
  assert remove_vowels("abcdef\nghijklm") == 'bcdf\nghjklm'  
  assert remove_vowels('fedcba') == 'fdcb'  
  assert remove_vowels('eeeee') == ''  
  assert remove_vowels('acBAA') == 'cB'  
  assert remove_vowels('EcBOO') == 'cB'  
  assert remove_vowels('ybcd') == 'ybcd'
output: def remove_vowels(s):
      vowels = 'aeiouAEIOU'
      return ''.join([char for char in s if char not in vowels])