build: Remove ffmpeg-full extension

It is not compatible with the 25.08beta freedesktop.org runtime base.
It was replaced by the codecs-extra extension which is auto-downloaded
with the runtime.

build-aux/org.gnome.Fractal.Devel.json

@@ -37,18 +37,6 @@
             "--share=network"
         ]
     },
-    "add-extensions": {
-        "org.freedesktop.Platform.ffmpeg-full": {
-            "version": "24.08",
-            "directory": "lib/ffmpeg",
-            "add-ld-path": ".",
-            "no-autodownload": false,
-            "autodelete": false
-        }
-    },
-    "cleanup-commands": [
-        "mkdir -p ${FLATPAK_DEST}/lib/ffmpeg"
-    ],
     "modules": [
         {
             "name": "grass",