test(snapshots): remove the parked snap-tests-todo tree (#2145)

The three cases (command-pack-watch-restart,
exit-non-zero-on-cmd-not-exists, pnpm-install-with-options) were parked
outside every runner: nothing in the repo references the directory and
no CI job executes it. The PTY suite already covers install-with-options
flows per package manager and command-not-found exits; recover the
watch-restart case from history if it becomes automatable.

Part of #2116.

Author: fengmk2