Use real API endpoints in documentation

There is no need to make the API endpoints environment-specific. But it
is still useful to know what the endpoint is.

Also fixes a broken link on the integration page.

app/main/views/send.py

@@ -209,7 +209,6 @@ def send_from_api(service_id, template_id):
         'views/send-from-api.html',
         template=template,
         payload=json.dumps(payload, indent=4),
-        api_host=current_app.config['API_HOST_NAME'],
         service_id=service_id
     )