Update manual page references and macros to align to mandoc syntax

xlocale.3: Comment out reference to atof_l(3), atoi_l(3), atol_l(3), atoll_l(3)

These manual page references do not exist.

lagg.4: Change the reference for /etc/rc.conf from a reference link

.Xr -> .Pa based on the context within the manual page it is used.

buf.9: Remove .Xr entries from the file

The buf.9 manual page contains a commented out .Xr reference.
The <filmmein> 9 entry is a placeholder and has been removed for
clarity.

Reviewed by: mhorne
Pull Request: https://github.com/freebsd/freebsd-src/pull/1114