Mk/bsd.port.mk: mark 14.3 unsupported

all: drop supoprt for FreeBSD 14.3

While here clean up some leftovers from FreeBSD 13

Reviewed by: adamw, jbeich, kirill_varnakov.com, saheed, sunpoet
Approved by: portmgr (implicit)
Differential Revision: https://reviews.freebsd.org/D57282