Revert "tool button: Use G_DEFINE_TYPE"
Revert "tool button: Use G_DEFINE_TYPE"

This reverts commit 4e56dfad0e33187d019c44ecfb5e7e99cf2da535.

It turns out that GtkToolButton is playing games with the class
pointer inside instance_init, so leave it alone.

alexlarsson/gtk,alexlarsson/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jigpu/gtk,alexlarsson/gtk,davidgumberg/gtk,davidgumberg/gtk,jadahl/gtk,jigpu/gtk,jadahl/gtk,davidgumberg/gtk,davidgumberg/gtk,grubersjoe/adwaita,jadahl/gtk,grubersjoe/adwaita,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,davidgumberg/gtk,alexlarsson/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,jadahl/gtk,jigpu/gtk,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,jigpu/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,jadahl/gtk,davidgumberg/gtk,jigpu/gtk,alexlarsson/gtk