Snippet of code to remove specific user actions on SharePoint online / Office 365. Handy if you decide later you don't want a script anymore. Make sure you scope it to web / site / list, in my example I was deploying the actions at site collection level and needed to remove it as it was slowing down the page load too much. 

 private static void RemoveCustomActions(ClientContext context)
        {
            Site site = context.Site;
            context.Load(site, x => x.UserCustomActions);
            context.ExecuteQuery();

            for (int i = 0; i < site.UserCustomActions.Count; i++)
            {
                if (site.UserCustomActions[i].ScriptSrc != null && site.UserCustomActions[i].ScriptSrc.Contains("bundle.js"))
                {
                    site.UserCustomActions[i].DeleteObject();
                    break;
                }
            }

            context.ExecuteQuery();
        }

Some of the example taken from: http://sharepoint.stackexchange.com/questions/164745/unable-to-unregister-usercustomactions-added-at-location-scriptlink-using-csom, this post also has a JScript example.