Remove a remaining unused piece of the old threading implementation (#3359)

This was missed in 6c0e21a5df.

h/static/scripts/render.coffee

-###*
-# @ngdoc service
-# @name render
-# @param {function()} fn A function to execute in a future animation frame.
-# @returns {function()} A function to cancel the execution.
-# @description
-# The render service is a wrapper around `window#requestAnimationFrame()` for
-# scheduling sequential updates in successive animation frames. It has the
-# same signature as the original function, but will queue successive calls
-# for future frames so that at most one callback is handled per animation frame.
-# Use this service to schedule DOM-intensive digests.
-###
-module.exports = ['$$rAF', ($$rAF) ->
-  cancel = null
-  queue = []
-
-  render = ->
-    return cancel = null if queue.length is 0
-    do queue.shift()
-    $$rAF(render)
-
-  (fn) ->
-    queue.push fn
-    unless cancel then cancel = $$rAF(render)
-    -> queue = (f for f in queue when f isnt fn)
-]