input: Write a python function to remove negative numbers from a list.
  assert remove_negatives([-1, 9, -3, 4, -8]) == [9, 4]
  assert remove_negatives([0, -1, -2, -3]) == []
  assert remove_negatives([3, -1, 2, -2, 0, 1]) == [3, 2, 1]
output: def remove_negatives(lst):
      return [x for x in lst if x >= 0]