input: Write a function that takes in a list of integers and removes all the duplicate elements from it. If the given list is empty then return an empty list.
  assert remove_duplicates([1, 2, 3, 2, 4, 5, 6, 3])==[1, 2, 3, 4, 5, 6]
  assert remove_duplicates([1, 1, 1, 1])==[1]
  assert remove_duplicates([2, 3, 4])==[2, 3, 4]
  assert remove_duplicates([])==[]
  assert remove_duplicates([5])==[5]
output: def remove_duplicates(lst):
      return list(dict.fromkeys(lst))