comms/fldigi: Fix plist and modernize Makefile

• Define LICENSE_FILE
• Remove dependency of (lib)Boost, the source code doesn't reference it at all
• Rearrange Makefile to closer follow Porters Handbook
• Drop native optimization option, rely on framework CPUTYPE variable instead
• Use framework _DESC
• Fix plist with NLS

PR: 276650
Approved by: hamradio (db)