Remove unused toggle from diff discussion diff headers

app/views/discussions/_diff_with_notes.html.haml

@@ -3,7 +3,7 @@
 
 .diff-file.file-holder
   .js-file-title.file-title
-    = render "projects/diffs/file_header", diff_file: diff_file, blob: blob, diff_commit: diff_file.content_commit, project: discussion.project, url: discussion_path(discussion)
+    = render "projects/diffs/file_header", diff_file: diff_file, blob: blob, diff_commit: diff_file.content_commit, project: discussion.project, url: discussion_path(discussion), show_toggle: false
 
   .diff-content.code.js-syntax-highlight
     %table

app/views/projects/diffs/_file_header.html.haml

-%i.fa.diff-toggle-caret.fa-fw
+- show_toggle = local_assigns.fetch(:show_toggle, true)
+
+- if show_toggle
+  %i.fa.diff-toggle-caret.fa-fw
+
 - if defined?(blob) && blob && diff_file.submodule?
   %span
     = icon('archive fw')