util.jid: refactor code a bit,
- Optimize split function
- Add function to obtain a single jid section
stanza_router: remove deprecated warnings, and use jid sectioning function.
hostmanager: optimize code by using jid sectioning function.
mod_{private/register_json}, pubsub_aux.lib: remove unused imports.
mam.lib, mod_mam: optimize code by using jid sectioning function.
mod_{component/disco/lastactivity/messagefilter/muc_log{_http}/pubsub}: follow previous commit...
mod_muc_limits: optimize using jid sectioning and fix call to jid_split (no traces, how?!).
mod_muc, muc.lib: optimize using jid sectioning and remove select() calls.