comms/flmsg: Update 4.0.23 => 4.0.24

Changelogs:

• https://sourceforge.net/p/fldigi/flmsg/ci/v4.0.24/tree/ChangeLog

• Switch MASTER_SITES to SourceForge
• Actualise WWW URI
• Improve pkg-descr

Approved by: hamradio@ (alven@, yuri@)
Approved by: yuri@ (Mentor)
Differential Revision: https://reviews.freebsd.org/D52969