Provide canned removal message for ATAS

[mdeuk]

We're seeing an uptick in "ATAS" related messages, which relate to individuals personal circumstances.

At the moment, the generic templates on Alaveteli don't cover the specific information that is helpful to convey to individuals, so it is time consuming to carry out admin actions on these requests.

We could, perhaps, use a variant of the setup for immigration related matters (body 93723).

[mdeuk]

I've added d5f6ee4 in pr #1823, which hopefully covers this off.