hil: remove the D-state/wedge containment that never fired (#4018)

Every "USB subsystem is wedged" verdict and pool abandon in CI logs came
from the usbtest new_id registry contention fixed by #3955; the markers,
post-pool recovery, strays and abandon exit never fired after it.

- usbtest confirms a hang by reaping its own child, then tries one
  recovery step; only the battery's JSON verdict latches board-wedged
- drop wedged-board markers, post-pool recovery, pool containment and
  the abandon path; keep the bounded pool drain and partial report
- trim the sysfs strand memo to the inode memo and its per-path cap
- keep convoy-safe flashers, flasher_recover and the manual
  usb-kernel-recover playbook