Purge only returned an error and nothing called it, so it is gone from
the ImageCache interface and from Service, along with its error value.
It can be added back when something needs it; eviction reclaims disk
space meanwhile. The SignatureValidator, Allowlist and Storage
interfaces in imgcache.go had no implementers and no users, and
described types that look different from the real ones, so they are
deleted. No behaviour changes.
Model: opus-5-5
clawbot