fixed-layout: Use the Actor iteration API
fixed-layout: Use the Actor iteration API

Forgot to migrate the FixedLayout layout manager like we did for the
other layout managers provided by Clutter.

ebassi/clutter,GNOME/clutter,djdeath/clutter-android,GNOME/clutter,collects/clutter,kerrickstaley/clutter-vala,djdeath/clutter,jigpu/clutter,heysion/clutter-clone,GNOME/clutter,ebassi/clutter,jigpu/clutter,djdeath/clutter,collects/clutter,jigpu/clutter,GNOME/clutter,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded,djdeath/clutter-multithreaded,djdeath/clutter-android,djdeath/clutter,Distrotech/clutter,jigpu/clutter,djdeath/clutter-multithreaded,djdeath/clutter-android,djdeath/clutter-multithreaded,djdeath/clutter-android,GNOME/clutter,djdeath/clutter,djdeath/clutter,heysion/clutter-clone,kerrickstaley/clutter-vala,collects/clutter,djdeath/clutter-android,ebassi/clutter,ebassi/clutter,djdeath/clutter,Distrotech/clutter,Distrotech/clutter,heysion/clutter-clone,kerrickstaley/clutter-vala,ebassi/clutter,heysion/clutter-clone,collects/clutter,Distrotech/clutter,Distrotech/clutter,heysion/clutter-clone,collects/clutter,Distrotech/clutter,jigpu/clutter,jigpu/clutter