Write a recursive function "otpu" ("upto" backwards)
// that takes two Int parameters "start" and "end" and produces a "List[Int]"
// that counts DOWN from "start" to "end" (inclusive at both ends) one at
// a time. If "start < end", the empty list must be returned.
def otpu (start:Int, end:Int) : List[Int] =
throw new Exception(" ")