Update content based on Thom’s feedback

On the page where signed in users can download the agreement:

> The second sentence of that could probably just be 'You can [download
> a copy]'. And could go at the end of the previous paragraph. (We try
> to avoid 'here', and the 'if you need to' is probably unnecessary).

On the page where we give users a choice of agreement to sign:

> We could probably edit that callout down a bit to: '[Contact us] if
> you're not sure whether your organisation is a crown or non-crown
> body.'
>
> (Try to keep callouts to a single sentence if we can)

app/templates/views/agreement-choose.html

@@ -34,9 +34,8 @@
     </p>
     <div class="panel panel-border-wide">
       <p>
-        Unsure whether your organisation is a crown body? Contact
-        <a href="{{ url_for('main.support') }}">support</a>
-        and we’ll help you work it out.
+        <a href="{{ url_for('main.support') }}">Contact us</a> if you’re
+        not sure whether your organisation is a crown or non-crown body.
       </p>
     </div>
     <h2 class="heading-small">