Revert "Fix compile on systems not using X11"

This reverts commit 316b59c9de49965b32d16098a740355cb8d7f10e.

Preparations to revert 56d67620f985ab58f62b93967887147f8c400f66.
Revert "#9631: Hint GNOME 3 window manager to use dark window borders"

This reverts commit 56d67620f985ab58f62b93967887147f8c400f66.

This never worked, as reported by the reporter. Likely the realize function is
being assigned after the window is already realized.