tests: prune some weed in a non-POSIX test Fixes automake bug#14494. * t/distcheck-pr10470.sh: Make sure the test-driver is installed. Adjust to run_make changes. Adjust grep pattern to match new output. Signed-off-by: Peter Rosin <peda@lysator.liu.se> Co-authored-by: Stefano Lattarini <stefano.lattarini@gmail.com>