atdts: ignore 'wrap' types

[mjambon]

The following should not produce an error:

$ cat toto.atd 
type t = int wrap
$ atdts toto.atd
Error: TODO: wrap

The wrap should be ignored as we do for example in the atdpy implementation.

[aryx]

it's atdts, not atdpy

[mjambon]

While we're at it, let's add an option to atdcat for removing all wraps. This offers a way to fix the problem for all backends. It's also good for diffs, educational, etc.