input: Write a function that takes in a list of integers and removes all the duplicate elements from it. The function should return the list of unique elements in the same order as they first appeared.
  assert remove_duplicates([1, 2, 3, 2, 4, 5, 6, 3])==[1, 2, 3, 4, 5, 6]
  assert remove_duplicates([4, 5, 4, 5, 5, 4])==[4, 5]
  assert remove_duplicates([7, 7, 7, 7, 7])==[7]
  assert remove_duplicates([])==[]
  assert remove_duplicates([3, 1, 2, 1, 2, 3])==[3, 1, 2]
output: def remove_duplicates(lst):
      seen = set()
      result = []
      for item in lst:
          if item not in seen:
              seen.add(item)
              result.append(item)
      return result