Partially revert "PERF: Improve query performance all inbox private messages. (#14304)" (#14344)

This partially reverts commit ddb458343dc39a7a8c99467dcd809b444514fe2c.

Seeing performance degrade on larger sites so back to drawing board on
this one. Instead of the DISTINCT LEFT JOIN, we switch back to
IN(subquery).

app/controllers/topics_controller.rb

@@ -973,7 +973,7 @@ class TopicsController < ApplicationController
 
     topic_ids = TopicsBulkAction.new(
       current_user,
-      topic_scope.distinct(false).pluck(:id),
+      topic_scope.pluck(:id),
       type: "dismiss_topics"
     ).perform!
 
@@ -1245,11 +1245,7 @@ class TopicsController < ApplicationController
     if inbox = params[:private_message_inbox]
       filter = private_message_filter(topic_query, inbox)
       topic_query.options[:limit] = false
-
-      topic_query
-        .filter_private_messages_unread(current_user, filter)
-        .distinct(false)
-        .pluck(:id)
+      topics = topic_query.filter_private_messages_unread(current_user, filter)
     else
       topics = TopicQuery.unread_filter(topic_query.joined_topic_user, staff: guardian.is_staff?).listable_topics
       topics = TopicQuery.tracked_filter(topics, current_user.id) if params[:tracked].to_s == "true"
@@ -1268,9 +1264,9 @@ class TopicsController < ApplicationController
       if params[:tag_name].present?
         topics = topics.joins(:tags).where("tags.name": params[:tag_name])
       end
-
-      topics.pluck(:id)
     end
+
+    topics.pluck(:id)
   end
 
   def private_message_filter(topic_query, inbox)