Deleting last elem of seq-zip produces nil
cljs.user=> (require '[clojure.zip :as zip])
cljs.user=> (-> '(1) zip/seq-zip zip/down zip/remove zip/root)
This should return the empty list. See CLJ-2616.
CLJS-3301.patch copies the essentials from CLJ-2616.
Perhaps we should wait and see if the patch in CLJ-2616 is accepted / lands.