input: Write a function to optimize the given Python code to use built-in functions for removing duplicates in an array. If the array is empty, return an empty array.
  assert removeDuplicates([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert removeDuplicates([5, 5, 5, 5]) == [5]
  assert removeDuplicates([]) == []
  assert removeDuplicates([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
output: def removeDuplicates(arr):
      return list(dict.fromkeys(arr))