input: Write a function that takes an array of strings and removes all duplicates, returning the resulting array.
  
  ### Example:
  
  assert removeDuplicates(['a', 'b', 'a', 'c', 'c', 'd'])==['a', 'b', 'c', 'd']
  assert removeDuplicates([])==[]
  assert removeDuplicates(['a', 'a', 'a', 'a'])==['a']
  assert removeDuplicates(['x', 'y', 'z', 'x', 'y', 'z'])==['x', 'y', 'z']
  
output: def removeDuplicates(arr):
      return list(dict.fromkeys(arr))