examples: Clean up the threads usage example
examples: Clean up the threads usage example

• Remove the threads_enter/leave calls; they are not needed, given that
  the code between init() and main() is single threaded.

• Ensure that the idle callbacks are inserted with the right priority,
  to avoid updating the UI after the data has been freed.

djdeath/clutter,ebassi/clutter,heysion/clutter-clone,GNOME/clutter,GNOME/clutter,djdeath/clutter,djdeath/clutter-android,collects/clutter,collects/clutter,djdeath/clutter-android,heysion/clutter-clone,Distrotech/clutter,ebassi/clutter,heysion/clutter-clone,djdeath/clutter,ebassi/clutter,GNOME/clutter,jigpu/clutter,jigpu/clutter,Distrotech/clutter,jigpu/clutter,heysion/clutter-clone,djdeath/clutter,Distrotech/clutter,jigpu/clutter,GNOME/clutter,Distrotech/clutter,GNOME/clutter,djdeath/clutter-android,heysion/clutter-clone,collects/clutter,djdeath/clutter,djdeath/clutter-android,djdeath/clutter-android,collects/clutter,Distrotech/clutter,ebassi/clutter,jigpu/clutter,ebassi/clutter,collects/clutter,Distrotech/clutter,jigpu/clutter,djdeath/clutter