input: Write a function to remove all duplicate elements from a list of integers. The function should return the new list with all duplicates removed.
  assert remove_duplicates([1, 2, 3, 2, 4, 5, 6, 3])==[1, 2, 3, 4, 5, 6]
  assert remove_duplicates([5, 5, 5, 5])==[5]
  assert remove_duplicates([])==[]
  assert remove_duplicates([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
  assert remove_duplicates([1, 1, 2, 2, 3, 3])==[1, 2, 3]
output: return list(set(lst))