kola/tests: Drop obsolete cl.update.grubnop test

The code to binary patch GRUB was dropped from update_engine some time
ago in flatcar/update_engine@e688113,
so it no longer makes sense to test this.

I would have also needed to update the test to handle xz compression now
that we are switching to that.

Signed-off-by: James Le Cuirot <[email protected]>