Fix an old bug in newsyslog where we kept one log file more than was

Fix an old bug in newsyslog where we kept one log file more than was
requested in newsyslog.conf.  This was only the case using the non-time
based filenames (.0, .1, .2 etc.).

The change also makes newsyslog clean clean up the old extra logfile so
users don't end up with a single stale logfile which won't be rotated
out.

This change also cleans up some code a bit to avoid more copy / paste
code and removes some old copy / paste code in the process.

PR:		bin/76697
MFC after:	2 weeks