bugfix: relax next verification

AUR renders its own 404 Not Found page when a bad route
is encountered. Introducing the previous verification
caused an error in this case when setting a language
while viewing the Not Found page. So, instead of checking
through routes, just make sure that the next parameter
starts with a '/' character, which removes the possibility
of any cross attacks.

+ Removed aurweb.asgi.routes; no longer needed.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/routers/html.py

@@ -32,11 +32,9 @@ async def language(request: Request,
     parameters across the redirect.
     """
     from aurweb.db import session
-    from aurweb.asgi import routes
-    if unquote(next) not in routes:
-        return HTMLResponse(
-            b"Invalid 'next' parameter.",
-            status_code=400)
+
+    if next[0] != '/':
+        return HTMLResponse(b"Invalid 'next' parameter.", status_code=400)
 
     query_string = "?" + q if q else str()