Remove thumb_url from Mattermost, and restore accidental deletion from Slack

lib/discourse_chat/provider/mattermost/mattermost_provider.rb

@@ -65,7 +65,6 @@ module DiscourseChat
           text: post.excerpt(SiteSetting.chat_integration_mattermost_excerpt_length, text_entities: true, strip_links: true, remap_emoji: true),
           title: "#{topic.title} #{(category == '[uncategorized]') ? '' : category} #{topic.tags.present? ? topic.tags.map(&:name).join(', ') : ''}",
           title_link: post.full_url,
-          thumb_url: post.full_url,
         }
 
         message[:attachments].push(summary)

lib/discourse_chat/provider/slack/slack_provider.rb

@@ -53,7 +53,8 @@ module DiscourseChat::Provider::SlackProvider
       text: excerpt(post),
       mrkdwn_in: ["text"],
       title: "#{topic.title} #{(category == '[uncategorized]') ? '' : category} #{topic.tags.present? ? topic.tags.map(&:name).join(', ') : ''}",
-      title_link: post.full_url
+      title_link: post.full_url,
+      thumb_url: post.full_url
     }
 
     message[:attachments].push(summary)