example: Drop Glade support

This is useless to the test application Flatpak and this will avoid
having to package gladeui when Glade support will be made more complex.
2 jobs for flatpak-glade in 4 minutes and 27 seconds (queued for 8 minutes and 38 seconds)
Status Name Job ID Coverage
  Build
passed build-debian #2966
librem5

00:02:10

24.9%
passed build-debian-package #2967
librem5

00:02:17