scrolled window: Drop unnecessary transient nodes
scrolled window: Drop unnecessary transient nodes

We already add the .frame style class to the context depending
on the shadow property. No need to save the context and add it
again all the time.

grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita