flow box: Avoid excessive signals
flow box: Avoid excessive signals

We were emitting the a11y ::selection-changed signal much more
often than ::selected-children-changed. Thats not necessary.

alexlarsson/gtk,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,davidgumberg/gtk,msteinert/gtk,Lyude/gtk-,jigpu/gtk,ahodesuka/gtk,Adamovskiy/gtk,grubersjoe/adwaita,msteinert/gtk,chergert/gtk,grubersjoe/adwaita,Lyude/gtk-,Adamovskiy/gtk,jigpu/gtk,Adamovskiy/gtk,jadahl/gtk,jadahl/gtk,Adamovskiy/gtk,Lyude/gtk-,ahodesuka/gtk,msteinert/gtk,alexlarsson/gtk,davidgumberg/gtk,davidgumberg/gtk,msteinert/gtk,jessevdk/gtk,davidgumberg/gtk,jadahl/gtk,jigpu/gtk,Adamovskiy/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,davidgumberg/gtk,Adamovskiy/gtk,Adamovskiy/gtk,alexlarsson/gtk,jessevdk/gtk,grubersjoe/adwaita,Lyude/gtk-,chergert/gtk,Sidnioulz/SandboxGtk,jigpu/gtk,ahodesuka/gtk,chergert/gtk,alexlarsson/gtk,alexlarsson/gtk,jessevdk/gtk,alexlarsson/gtk,Lyude/gtk-,jadahl/gtk,grubersjoe/adwaita,chergert/gtk,msteinert/gtk,grubersjoe/adwaita,Sidnioulz/SandboxGtk,chergert/gtk,ahodesuka/gtk,chergert/gtk,davidgumberg/gtk,jessevdk/gtk,Lyude/gtk-,msteinert/gtk,jessevdk/gtk,davidgumberg/gtk,chergert/gtk,jigpu/gtk,jadahl/gtk,Sidnioulz/SandboxGtk,jessevdk/gtk,jadahl/gtk,jadahl/gtk,Sidnioulz/SandboxGtk,ahodesuka/gtk,alexlarsson/gtk,ahodesuka/gtk,jessevdk/gtk,Lyude/gtk-,jigpu/gtk,jadahl/gtk,Lyude/gtk-,grubersjoe/adwaita,grubersjoe/adwaita,Sidnioulz/SandboxGtk,ahodesuka/gtk,jigpu/gtk,alexlarsson/gtk,chergert/gtk,Adamovskiy/gtk