input: Write a function to remove all consecutive duplicates from a given string and return the modified string.
  def remove_duplicates(string):
      result = ""
      prev = ''
      for char in string:
          if char != prev:
              result += char
              prev = char
      return result
  
  assert remove_duplicates("AAABBCCCD") == "ABCD"
  assert remove_duplicates("AABBBCDDD") == "ABCD"
  assert remove_duplicates("ABBCCCDDDEEEF") == "ABCDEF"
  assert remove_duplicates("ABC") == "ABC"
  assert remove_duplicates("") == ""
output: def remove_duplicates(string):
      result = ""
      prev = ''
      for char in string:
          if char != prev:
              result += char
              prev = char
      return result