gtk-demo: Remove the popover demo
It doesn't work anymore, since popovers now need support in the parent, and we don't really need a demo just for popovers. They are used everywhere already.
Fixes: #2429 (closed)
It doesn't work anymore, since popovers now need support in the parent, and we don't really need a demo just for popovers. They are used everywhere already.
Fixes: #2429 (closed)