debug repl tests: Add visibility, remove test that times out

The 'Can't backtrace now' message takes over 10 seconds to return.
That's too much time to have to wait for a test, and when it times
out, it was causing an orphaned node process.

This cleans up the node process, and also removes the test that's
timing out, so that the case is hit less often.

Todo: Make the backtrace message come back faster.