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 with all unique elements in the original order.
  assert remove_duplicates([1, 2, 3, 2, 4, 5, 6, 3])==[1, 2, 3, 4, 5, 6]
  assert remove_duplicates([4, 4, 4, 4])==[4]
  assert remove_duplicates([1, 1, 2, 2, 3, 3])==[1, 2, 3]
  assert remove_duplicates([])==[]
  assert remove_duplicates([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
output: def remove_duplicates(lst):
      seen = set()
      result = []
      for num in lst:
          if num not in seen:
              seen.add(num)
              result.append(num)
      return result