welcome tour: replace yelp with gnome-tour

this replaces calling yelp at startup by tour
https://gitlab.gnome.org/GNOME/gnome-tour
2 jobs for bilelmoussaoui/yelp-to-tour in 6 minutes and 50 seconds
Status Job ID Name Coverage
  Build
passed #807278
build-maximal

00:05:39

passed #807277
build-minimal

00:06:50