client/posts: remove cache buster query string on post file change

Since filenames now use the new file's sha1.

client/js/controls/post_content_control.js

@@ -88,7 +88,6 @@ class PostContentControl {
 
     _evtPostContentChange(e) {
         this._post = e.detail.post;
-        this._post.mutateContentUrl();
         this._reinstall();
     }
 

client/js/models/post.js

@@ -454,13 +454,6 @@ class Post extends events.EventTarget {
             });
     }
 
-    mutateContentUrl() {
-        this._contentUrl =
-            this._orig._contentUrl +
-            "?bypass-cache=" +
-            Math.round(Math.random() * 1000);
-    }
-
     _updateFromResponse(response) {
         const map = () => ({
             _version: response.version,