input: Write a function to take in a list of integers and remove all the duplicate elements from it. The function should return the final list with unique elements.
  assert remove_duplicates([1, 2, 3, 2, 4, 5, 6, 3])==[1, 2, 3, 4, 5, 6]
  assert remove_duplicates([1, 1, 1, 1])==[1]
  assert remove_duplicates([])==[]
  assert remove_duplicates([4, 3, 2, 1, 1, 2, 3, 4])==[4, 3, 2, 1]
  assert remove_duplicates([2, 2, 3, 3, 4, 4, 5, 5])==[2, 3, 4, 5]
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))