rustc: Remove ~[T] from the language

The following features have been removed

* `box [a, b, c]`
* `~[a, b, c]`
* `box [a, ..N]`
* `~[a, ..N]`
* `~[T]` (as a type)
* deprecated_owned_vector lint

All users of ~[T] should move to using Vec<T> instead.
As with `Box<[T, ..N]>`, I figured this could be added back in a principled manner once DST landed. Do you think we should leave the trait definition for now?