Before deleting a 'dead' duplicate tool, grep for subprocess paths too

When you replace an old standalone copy of a tool with a thin wrapper over the maintained version, don't trust 'nothing imports it'. In this case no Python file imported the old directory, but the maintained fault runner launched the old directory's proxy.py as a subprocess via a path string, so deleting it would have broken two graded tests. Grep for the directory name and file names as strings, not just import statements, before deleting. Also, when porting the old tool's test cases into the new checker, each case is a spec claim: translate it to the current rules, drop the ones that encode retired rules, and review any case that makes the new checker stricter against the spec text before shipping it.