Revert "csd: Drop the GTK_FRAME_EXTENTS requirement"
Revert "csd: Drop the GTK_FRAME_EXTENTS requirement"

This reverts commit fb9a6bb6d8d6b60b25c9b9853decbcea938f7863.

In a recent test, I've found that Xfce and Mate now support
this, so they will not be affected by this requirement. And
adding the check back will solve the 'client-side shadow'
problem in KDE.

jigpu/gtk,alexlarsson/gtk,davidgumberg/gtk,Adamovskiy/gtk,ahodesuka/gtk,davidgumberg/gtk,jigpu/gtk,jigpu/gtk,ahodesuka/gtk,alexlarsson/gtk,chergert/gtk,Lyude/gtk-,Lyude/gtk-,chergert/gtk,Lyude/gtk-,jadahl/gtk,davidgumberg/gtk,jadahl/gtk,alexlarsson/gtk,Adamovskiy/gtk,chergert/gtk,jigpu/gtk,jadahl/gtk,chergert/gtk,ahodesuka/gtk,alexlarsson/gtk,Adamovskiy/gtk,alexlarsson/gtk,alexlarsson/gtk,davidgumberg/gtk,Lyude/gtk-,alexlarsson/gtk,Lyude/gtk-,davidgumberg/gtk,grubersjoe/adwaita,Adamovskiy/gtk,Lyude/gtk-,jadahl/gtk,ahodesuka/gtk,Adamovskiy/gtk,chergert/gtk,chergert/gtk,jadahl/gtk,jigpu/gtk,Lyude/gtk-,Adamovskiy/gtk,alexlarsson/gtk,grubersjoe/adwaita,jadahl/gtk,chergert/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jigpu/gtk,grubersjoe/adwaita,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,ahodesuka/gtk,grubersjoe/adwaita,chergert/gtk,ahodesuka/gtk,jigpu/gtk,grubersjoe/adwaita,davidgumberg/gtk,ahodesuka/gtk,Lyude/gtk-,grubersjoe/adwaita,jadahl/gtk,Adamovskiy/gtk,grubersjoe/adwaita,ahodesuka/gtk,davidgumberg/gtk