testsuite: Remove dangling references to box-packing tests
These were removed in commit c47abb5f, before 3.96.0.
Found while updating the GTK 4 pre-release in Debian experimental to 3.96.
These were removed in commit c47abb5f, before 3.96.0.
Found while updating the GTK 4 pre-release in Debian experimental to 3.96.