Fix flatpak manifest

Closed Lionir Deadman requested to merge lionirdeadman/gnome-maps:master into master

Just coming to fix the flatpak manifest. Updating libical for the sake of it, removing libgee because we don't need to build it ourselves and change libgfbgraph from git to latest stable since maps complains otherwise since they're prepping up 0.3.0 which has breaking changes.

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