Remove use of deprecated GtkVBox API in GTK+ example
Remove use of deprecated GtkVBox API in GTK+ example

RevBy: TrustMe
When building with recent GTK+ 3.0 and CONFIG+=debug
this will cause the build to fail.

Elleo/framework,RHawkeyed/framework,jpetersen/framework,binlaten/framework,jpetersen/framework,RHawkeyed/framework,Elleo/framework