run: Update note on seccomp filter code sharing

This comment needs to be modernized for 2025. It notably fails to
mention the two projects that are actually still using code that looks
like Flatpak's.

common/flatpak-run.c

@@ -1886,34 +1886,22 @@ setup_seccomp (FlatpakBwrap   *bwrap,
 
   /**** BEGIN NOTE ON CODE SHARING
    *
-   * There are today a number of different Linux container
-   * implementations.  That will likely continue for long into the
-   * future.  But we can still try to share code, and it's important
-   * to do so because it affects what library and application writers
-   * can do, and we should support code portability between different
-   * container tools.
+   * This code was originally part of the obsolete linux-user-chroot project,
+   * which was itself heavily influenced by Sandstorm's seccomp filters.
+   * Nowadays, the canonical upstream location for this code is Flatpak:
    *
-   * This syscall blocklist is copied from linux-user-chroot, which was in turn
-   * clearly influenced by the Sandstorm.io blocklist.
+   *   https://github.com/flatpak/flatpak/blob/main/common/flatpak-run.c
    *
-   * If you make any changes here, I suggest sending the changes along
-   * to other sandbox maintainers.  Using the libseccomp list is also
-   * an appropriate venue:
-   * https://groups.google.com/forum/#!forum/libseccomp
+   * Here is a list of projects that have directly copied Flatpak's sandbox
+   * filters. These projects aim to exactly or almost exactly match what Flatpak
+   * is doing, so we almost always need to update them whenever the code here is
+   * touched:
    *
-   * A non-exhaustive list of links to container tooling that might
-   * want to share this blocklist:
+   *   https://github.com/WebKit/WebKit/blob/main/Source/WebKit/UIProcess/Launcher/glib/BubblewrapLauncher.cpp
+   *   https://gitlab.gnome.org/GNOME/gnome-desktop/-/blob/master/libgnome-desktop/gnome-desktop-thumbnail-script.c
    *
-   *  https://github.com/sandstorm-io/sandstorm
-   *    in src/sandstorm/supervisor.c++
-   *  https://github.com/flatpak/flatpak.git
-   *    in common/flatpak-run.c
-   *  https://git.gnome.org/browse/linux-user-chroot
-   *    in src/setup-seccomp.c
-   *
-   * Other useful resources:
-   * https://github.com/systemd/systemd/blob/HEAD/src/shared/seccomp-util.c
-   * https://github.com/moby/moby/blob/HEAD/profiles/seccomp/default.json
+   * (We perhaps ought to split this code out of Flatpak into a subproject, to
+   * make code sharing easier and reduce the need for manual copy/pasting.)
    *
    **** END NOTE ON CODE SHARING
    */