Install {cron.d,newsyslog.conf.d,syslog.d} via make distribution, not make install

I incorrectly started this pattern in r277541 with the opensm newsyslog.conf.d file,
and continued using it in r318441 and r318443.

This will fix the files being handled improperly via installworld, preventing tools like
etcupdate, mergemaster, etc from functioning properly when comparing the installed
contents on a system vs the contents in a source tree when doing merges.

PR: 219404
Submitted by: Dan McGregor <dan.mcgregor@usask.ca>
MFC after: 2 weeks
MFC with: r277541, r318441, r318443
Sponsored by: Dell EMC Isilon