Remove manpages from OLD_FILES

Remove apm.8 and apmconf.8 from OLD_FILES in the relevant Makefiles.

These pages are now installed unconditionally as per 0a0f7486413c

PR: 257228
Reported by: yasu@utahime.org, wosch@
Approved by: imp@, wosch@
Fixes: 0a0f7486413c - Build manpages for all architectures
MFH: 4 weeks
Differential Revision: https://reviews.freebsd.org/D31256