SI-7294 Treat TupleN as final under -Xfuture

For the purposes of checkability warnings. This will
warn in case of:

	scala> (1, 2) match { case Seq() => 0; case _ => 1 }
	res9: Int = 1

Given how often Tuples are used as scrutinees, this is
a highly desirable place to warn.

I was orginally going to unlock this under -Xlint, and
could be easily convinced to go that way, given that
-Xfuture is a less popular option.
SI-7294 Deprecate inheritance from TupleN.

The motivation is to provide static warnings
in cases like:

    scala> (1, 2) match { case Seq() => 0; case _ => 1 }
    res9: Int = 1
Cleanup obsolete options in CodeGen.