fb_posts: past its publish time, a scheduled post reads as published

Facebook does not call back and the reconciliation was never built, so a
row that stayed scheduled forever was a lie of omission. Decided by Mike:
once the time passes with nothing else reported, the post is published.
status keeps what the publisher last said; state is what a reader acts
on, and the open-only list and cancel use state. Cancel on a post whose
time has passed says so.

app/admin_api.py

@@ -1025,8 +1025,9 @@ def cancel_fb_post(request: Request, pid: str, x_admin_token: str = Header(None)
     rec = store.get_fb_post(pid)
     if not rec:
         raise HTTPException(404, "no such post")
-    if rec["status"] not in ("scheduled",):
-        raise HTTPException(409, "post is %s, not scheduled" % rec["status"])
+    if rec["state"] != "scheduled":
+        raise HTTPException(409, "post is %s, not scheduled" % rec["state"]
+                            + (" (its publish time has passed)" if rec["status"] == "scheduled" else ""))
     if not rec.get("cancel_url"):
         raise HTTPException(409, "no cancel link was recorded for this post")
     import urllib.request as _ur, urllib.error as _ue