♻️ Refactor workspace thumbails (again)

We probably need a counter of number of types this
code was refactored hehe

frontend/src/app/util/imposters.cljs

@@ -1,15 +0,0 @@
-;; This Source Code Form is subject to the terms of the Mozilla Public
-;; License, v. 2.0. If a copy of the MPL was not distributed with this
-;; file, You can obtain one at http://mozilla.org/MPL/2.0/.
-;;
-;; Copyright (c) KALEIDOS INC
-
-(ns app.util.imposters)
-
-;; This is needed to avoid a circular dependency between
-;; app.main.ui.workspace.shapes.frame and app.util.imposters
-(defonce render-fn (atom nil))
-
-(defn init!
-  [fn]
-  (reset! render-fn fn))