Remove ffmpeg cleanup command

Thanks to @yakushabb again for making this change in the Flathub
manifest:
flathub/io.github.wartybix.Constrict#9

Author: Wartybix

io.github.wartybix.Constrict.Devel.json

@@ -17,9 +17,6 @@
         "append-path" : "/usr/lib/sdk/rust-stable/bin",
         "build-args": ["--share=network"]
     },
-    "cleanup-commands" : [
-        "mkdir -p ${FLATPAK_DEST}/lib/ffmpeg"
-    ],
     "cleanup" : [
         "/include",
         "/lib/pkgconfig",