[RFC] Remove old/stale elements and GTK3 apps

[Kazhnuz]

GTK4 and Libadwaita are here for several years, so remove gtk3 apps for the list. The idea is that they'll be readded once they convert to GTK4. I'm not 100% sure this is yet the time to do that, but it might be ? I mean, at a same time we remove some important apps, but it's usefull to make sure the list contain apps that are up the the current vision of GNOME (not the exact version, as they might not have every latest libadwaita widget, but they will be roughly up to standards). This is an RFC in the case people disagree with the idea.

Also remove some extensions and stuff, as we often do when they're old.

TODO

• [x] Finish removing every gtk3 apps
• [x] Remove some staled extension
• [x] Change the rules to require gtk4 and libadwaita apps.

[loicreynier]

I think libadwaita is sufficiently mature to remove non-GTK4 apps. I agree with the idea that the list should focus on applications that are up to date with the current GNOME version.

Additionally, GTK3 apps can be found in Awesome GTK if necessary.