DEV: Remove buffered-render file

This is the last and final commit in a multi-commit refactor to remove
all uses of buffered-render.

Previous commit: fc94b6cb9ee709a6744dc0da477f4a37e43d37e4 in this
series.

app/assets/javascripts/discourse-common/lib/buffered-render.js.es6

@@ -1,46 +0,0 @@
-import { scheduleOnce } from "@ember/runloop";
-// Ember 2.0 removes buffered rendering, but we can still implement it ourselves.
-// In the long term we'll want to remove this.
-
-const Mixin = {
-  _customRender() {
-    if (!this.element || this.isDestroying || this.isDestroyed) {
-      return;
-    }
-
-    const buffer = [];
-    this.buildBuffer(buffer);
-    this.element.innerHTML = buffer.join("");
-  },
-
-  rerenderBuffer() {
-    scheduleOnce("render", this, this._customRender);
-  }
-};
-
-export function bufferedRender(obj) {
-  if (!obj.buildBuffer) {
-    Ember.warn("Missing `buildBuffer` method", {
-      id: "discourse.buffered-render.missing-build-buffer"
-    });
-    return obj;
-  }
-
-  const caller = {};
-
-  caller.didRender = function() {
-    this._super(...arguments);
-    this._customRender();
-  };
-
-  const triggers = obj.rerenderTriggers;
-  if (triggers) {
-    caller.init = function() {
-      this._super(...arguments);
-      triggers.forEach(k => this.addObserver(k, this.rerenderBuffer));
-    };
-  }
-  delete obj.rerenderTriggers;
-
-  return Ember.Mixin.create(Mixin, caller, obj);
-}