input: Write a function that takes in a list of integers and removes all the duplicate elements from it, returning the list with unique elements only.
  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, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
  assert remove_duplicates([])==[]
  assert remove_duplicates([7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8])==[7, 8]
output: def remove_duplicates(lst):
      return list(set(lst))