extdir automatic releases ignore unpublished nodes
Reported by @artfulrobot
"Each day the system generates a new release node for GoCardless 1.10.0beta (it's configured to do this as a draft because the ext requires packaging, if that makes a difference). I have no way (except for trawling emails) to find a list of all the nodes, but basically they all need deleting; beta testers have downloaded from github so I don't need it released."