First stage of removing the chatlog subsystem that writes plain-text
per-day message logs to $XDG_DATA_HOME/profanity/chatlogs/. These files
were never read back by Profanity (history replay reads from the
database via log_database_get_previous_chat), so the feature only ever
wrote to disk for users to inspect with external tools.
This change reduces chatlog.c to no-op stubs, preserving all public
signatures so the ~20 call sites in event/, otr/ and profanity.c
continue to compile and link unchanged. Subsequent stages will remove
the call sites, the related preferences (PREF_CHLOG, PREF_GRLOG and the
per-encryption PREF_*_LOG) and the now-dead commands (/logging,
/otr log, /pgp log, /omemo log, /ox log).
Database-based history (PREF_DBLOG, /history) and the debug log
(log.c, /log) are unaffected.
