mod_pubsub_summary: Use pre-escaped UTF-8 sequence for compat This silences a warning about using the non-existent global 'utf8' each time this line was hit. The utf8 library was introduced in Lua 5.3, so the warning would appear with 5.1 and 5.2.

This module discards typing notifications sent to a bare host JID,
preventing error replies to be sent. These errors are harmless but can
be annoying sometimes if your client shows them prominently.