Drop FreeBSD < 14.0-BETA5 <sys/timerfd.h> workarounds

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=273373
https://cgit.freebsd.org/src/commit/?h=releng/14.0&id=7454117918cd
https://lists.freebsd.org/archives/freebsd-stable/2023-October/001533.html
Old -CURRENT, -STABLE, -RELENG snapshots were never supported in ports/.

This reverts commit 4458b6d2.
This reverts commit f2959034.
This reverts commit d7c83034.
This reverts commit 57256007.
This reverts commit f4c28b48.
This reverts commit 16392866.
This reverts commit b8948f86.
This reverts commit 5e70841f.
This reverts commit 600ca97f.