Removed fallback to clicked count for opened count

fixes https://github.com/TryGhost/Team/issues/2189

We don't want this fallback because the table on the analytics page will be empty while the count be higher than zero

ghost/core/core/server/api/endpoints/utils/serializers/output/mappers/posts.js

@@ -111,10 +111,7 @@ module.exports = async (model, frame, options = {}) => {
 
     if (jsonModel.email && jsonModel.count) {
         jsonModel.email.opened_count = Math.min(
-            Math.max(
-                jsonModel.email.opened_count || 0,
-                jsonModel.count.clicks || 0
-            ),
+            jsonModel.email.opened_count || 0,
             jsonModel.email.email_count
         );
     }