Include gstfdkaac in main app

[wjt]

See https://github.com/flathub/org.gnome.Totem.Devel/issues/25 for my goal here :)

[flathubbot]

Started test build 78978

[flathubbot]

Started test build 78983

[flathubbot]

Build 78978 successful To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/61572/org.gnome.Totem.Devel.flatpakref

[flathubbot]

Build 78983 successful To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/61577/org.gnome.Totem.Devel.flatpakref

[wjt]

Superseded by #28.