all: drop support for EOL FreeBSD 14.1

• Mk/bsd.port.mk: de-support FreeBSD 14.1
• devel/boost-libs: simplify a comment
• devel/libdispatch: remove a commented out and outdated code block
• editors/imhex: simplify some tautologies
• editors/libreoffice: remove an outdated BROKEN
• graphics/dspdfviewer: simplify OSVERSION logic

Approved by: portmgr (implicit)
Differential Revision: https://reviews.freebsd.org/D49099