mod_http_muc_log: Remove dead code This might be something left over since a different variant where the loop went like `for n = i-1, i-100, -1 do ... end` i.e. it went trough a fixed number of items instead of all the page until the current message. Then it would have needed something to stop going over the end, but since the checks are simple it shouldn't be much of a problem looping over even a very busy day.

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.