input: Write a function to remove all the duplicate elements from a list of integers. The function should return a new list with only unique elements.
  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([]) == []
  assert remove_duplicates([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
output: def remove_duplicates(lst):
      return list(set(lst))