Bug#1042912: Merge the Debian-specific desktop file with the upstream one

Upstream desktop file in version 115.1.1: https://salsa.debian.org/mozilla-team/thunderbird/-/blob/debian/sid/comm/taskcluster/docker/tb-flatpak/org.mozilla.Thunderbird.desktop

Bug#1042912: Merge the Debian-specific desktop file with the upstream one

Package: thunderbird Version: 1:115.0.1-2 Hallo Carsten, Upstream now provides a desktop file as part of their Flatpak distribution: https://salsa.debian.org/mozilla-team/thunderbird/- /blob/debian/experimental/comm/taskcluster/docker/thunderbird- flatpak/org.mozilla.Thunderbird.desktop