:advanced optimization not removing dead code

client.cljs

(ns example
  #_(:require [plumbing.core]))

(defn- map-kv [kf vf m]
  (persistent!
   (reduce (fn [result [k v]]
             (assoc! result (kf k) (vf v)))
           (transient {})
           m)))

(defn map-keys [f m]
  (map-kv f identity m))

#_(.log js/console (plumbing.core/map-keys inc {1 "foo" 2 "bar"}))
(.log js/console (map-keys inc {1 "foo" 2 "bar"}))

project.clj

(defproject test "0.1.0-SNAPSHOT"
  :description "FIXME: write this!"
  :url "http://example.com/FIXME"
  :dependencies [[org.clojure/clojure "1.5.1"]
                 [org.clojure/clojurescript "0.0-2156"]
                 [ring "1.2.1"]
                 [prismatic/plumbing "0.4.1"]]
  :plugins [[lein-cljsbuild "1.0.2"]
            [lein-ring "0.8.10"]]
  :hooks [leiningen.cljsbuild]
  :source-paths ["src/clj"]
  :cljsbuild {
    :builds {
      :main {
        :source-paths ["src/cljs"]
        :compiler {:output-to "resources/public/js/cljs.js"
                   :optimizations :advanced
                   :pretty-print false}
        :jar true}}}
  :main test.server
  :ring {:handler test.server/app})