Remove flatpak manifest

It now lives in flathub repo and will be maintained there

Packaging/nix/org.diasurgical.DevilutionX.yml

@@ -1,44 +0,0 @@
-app-id: org.diasurgical.DevilutionX
-runtime: org.freedesktop.Platform
-runtime-version: '22.08'
-sdk: org.freedesktop.Sdk
-command: devilutionx
-rename-desktop-file: devilutionx.desktop
-rename-appdata-file: devilutionx.metainfo.xml
-rename-icon: devilutionx
-
-finish-args:
-    - --socket=fallback-x11
-    - --socket=wayland
-    - --device=dri
-    - --share=network
-    - --share=ipc
-    - --socket=pulseaudio
-modules:
-    - name: devilutionX
-      buildsystem: cmake-ninja
-      config-opts:
-        - -DBUILD_TESTING=OFF
-        - -DCMAKE_BUILD_TYPE=Release
-      sources:
-        - type: archive
-          url: https://github.com/diasurgical/devilutionX/releases/download/1.5.0/devilutionx-src-fully-vendored.tar.xz
-          sha256: 18aee4324c71198a26f15fe2b342552411c2f62039b64cf9b2fa3e249f1bc4f9
-        # CJK fonts
-        - type: file
-          filename: fonts.mpq
-          url: https://github.com/diasurgical/devilutionx-assets/releases/download/v3/fonts.mpq
-          sha256: 6b62e03c42ae4427055e0f292a1beafb5e840c397adaf1f641b909be37b8653e
-          size: 58488019
-        # Diablo shareware demo
-        - type: file
-          filename: spawn.mpq
-          url: https://github.com/diasurgical/devilutionx-assets/releases/download/v3/spawn.mpq
-          sha256: 64427cd7c1ba904eaa2e0031c16a6b136d0ecef9abc888c5ff8344b459356e38
-          size: 25448219
-      post-install:
-        - "sed -i 's/Icon=devilutionx-hellfire/Icon=org.diasurgical.DevilutionX-hellfire/g' ${FLATPAK_DEST}/share/applications/devilutionx-hellfire.desktop"
-        - "mv ${FLATPAK_DEST}/share/applications/devilutionx-hellfire.desktop ${FLATPAK_DEST}/share/applications/${FLATPAK_ID}-hellfire.desktop"
-        - "mv ${FLATPAK_DEST}/share/icons/hicolor/512x512/apps/devilutionx-hellfire.png ${FLATPAK_DEST}/share/icons/hicolor/512x512/apps/${FLATPAK_ID}-hellfire.png"
-        - "mv fonts.mpq ${FLATPAK_DEST}/share/diasurgical/devilutionx"
-        - "mv spawn.mpq ${FLATPAK_DEST}/share/diasurgical/devilutionx"