Inspector backend hack
GtkSpinButton: Set the screen on the panel contexts

Failure to do so results in custom styling leaking through in
the inspector. This is pretty obvious, now that the inspector
is using a separate display connection and is generally isolated
from style changes.
Revert "Inspector backend hack"

This reverts commit f88a5dc8c78e6530baeebb6cba75fe3061926052.

Didn't mean to push this.