util.xml: Deduplicate handlers for restricted XML
Makes the code more like util.xmppstream, allowing easier comparisons if
we ever need to apply fixes in the future.
The Prosody project is open to contributions (see HACKERS file), but is
maintained daily by:
- Matthew Wild (mail: matthew [at] prosody.im)
- Waqas Hussain (mail: waqas [at] prosody.im)
- Kim Alvefur (mail: zash [at] prosody.im)
You can reach us collectively by email: developers [at] prosody.im
or in realtime in the Prosody chatroom: prosody@conference.prosody.im