Remove unnecessary loading of discussions in `IssuesController#show`

Discussions are now done asynchronously via the `IssuesController#discussions`
endpoint, so this should no longer be needed. This was taking 32% of the load
time for GitLab CE issue 1.

Closes #38034

app/controllers/projects/issues_controller.rb

@@ -71,9 +71,6 @@ class Projects::IssuesController < Projects::ApplicationController
     @noteable = @issue
     @note     = @project.notes.new(noteable: @issue)
 
-    @discussions = @issue.discussions
-    @notes = prepare_notes_for_rendering(@discussions.flat_map(&:notes), @noteable)
-
     respond_to do |format|
       format.html
       format.json do

changelogs/unreleased/sh-stop-loading-issue-discussions.yml

+---
+title: Remove unnecessary loading of discussions in `IssuesController#show`
+merge_request:
+author:
+type: fixed