mail/sympa: Update 6.2.78 => 6.2.80

Changelog:
https://github.com/sympa-community/sympa/blob/6.2.80/NEWS.md

Improve port:

• Remove unnecessary GNU_CONFIGURE_MANPREFIX.
• Remove unused ICONSDIR.
• Fix antipattern BUILD_DEPENDS=RUN_DEPENDS.
• Fix warning from portclippy.

PR: 298519 283227
Sponsored by: UNIS Labs (vvd, improve port)
Co-authored-by: Vladimir Druzenko <vvd@FreeBSD.org>
MFH: 2026Q3

(cherry picked from commit 00e774dc9c7575932f14bd8bdfde7619935e8e67)