input: Write a function to optimize the given Python code to use built-in functions. The original function removes duplicates from an array using nested loops. If the given array is empty then 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])==[5]
  assert removeDuplicates([])==[]
  assert removeDuplicates([1, 3, 2, 1, 3, 2])==[1, 3, 2]
  assert removeDuplicates([10, 10, 20, 30, 20])==[10, 20, 30]
output: def removeDuplicates(arr):
      return list(dict.fromkeys(arr))