chore: remove unreachable condition

Now that Python validates the addresses more strictly, we won't hit the
condition any longer.

If we wish to preserve this condition, we could also pass `strict=False`
to `getaddresses()`, but that seems to be counter to our desire of
having a valid email address.

Refs: python/cpython#123766

Signed-off-by: Mike Fiedler <miketheman@gmail.com>

warehouse/rss/views.py

@@ -40,8 +40,6 @@ def _format_author(release):
             return None
         author_emails.append(author_email)
 
-    if not author_emails:
-        return None
     return ", ".join(author_emails)