Remove `Observer[T]` from `Ivar[T]` type.
Remove `Observer[T]` from `Ivar[T]` type.

storm-enroute/reactors,reactors-io/reactors,storm-enroute/reactors,reactors-io/reactors,storm-enroute/reactors,reactors-io/reactors,storm-enroute/reactive-collections,reactors-io/reactors,storm-enroute/reactors