Remove vxml

[sammachin]

With the shutdown of the call API the link:vxml and unlink:vxml commands should be removed as it is no longer used.

There may be other places that it is referenced for example in the verbose numbers list screen where it shows if a number is linked to vxml but I would suggest leaving this for now as users may want to see that a number is still linked to vxml in order to identify changes.

[seanprashad]

Hey! I've opened a PR for this and would love a review if possible 😄