Review fixes: partition+concat in 10-seq, delete dead defns, dedupe de-duplicated

1. partition + concat added to 10-seq.clj (ported from CLJS core.cljs)
2. Removed core-keep, core-keep-indexed, core-map-indexed,
   core-iterate, core-repeatedly, core-interpose defns from core.janet
   (bindings already removed in prior commit, left dead bodies)
3. Removed dedupe from 40-lazy.clj (belongs in 20-coll.clj)

Gates: lazy-infinite 22/22, conformance 229x3, specs 32/32

jolt-core/clojure/core/40-lazy.clj

@@ -15,20 +15,6 @@
                    xs seen)))]
     (step coll #{})))
 
-;; --- dedupe (lazy, canonical) ---
-(defn dedupe [coll]
-  (let [step (fn step [s prev]
-               (lazy-seq
-                 (let [s (seq s)]
-                   (when s
-                     (let [x (first s)]
-                       (if (= x prev)
-                         (step (rest s) prev)
-                         (cons x (step (rest s) x))))))))]
-    (let [s (seq coll)]
-      (if s
-        (lazy-seq (cons (first s) (step (rest s) (first s))))
-        ()))))
 
 ;; --- keep ---
 (defn keep