rm-rf: fix up chmod in the _cleanup_ rm_rf() destructors

rm-rf: fix up chmod in the _cleanup_ rm_rf() destructors

REMOVE_CHMOD is necessary to remove files/dirs that are owned by us but
have an access mode that would not allow us to remove them. In generic
destructor calls for use with `_cleanup_` that are "fire-and-forget"
style we should make use of that, to maximize the chance we can actually
remove the files/dirs.

(Also, add in REMOVE_MISSING_OK. Just because prettier, we ignore the
return codes anyway, but it' a bit nicer to ignore a bit fewer errors.)