net-im/flare: update to 0.16.3

While here:

• Moved some of the *_DEPENDS into USE_GNOME and removed excess.
• Improve COMMENT.
• Improve pkg-descr.
• Marked python dependency only for build because it's only needed for build.

Changelogs:
https://gitlab.com/schmiddi-on-mobile/flare/-/releases/0.16.2
https://gitlab.com/schmiddi-on-mobile/flare/-/releases/0.16.3

PR: 287920
Reported by: Yusuf Yaman <nxjoseph@protonmail.com> (maintainer)