Use proper classes for sdiff content

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/projects/notes/_discussion.html.haml

@@ -36,18 +36,14 @@
   .discussion-body
     - if note.for_diff_line?
       - if note.active?
-        .content
-          .file= render "projects/notes/discussion_diff", discussion_notes: discussion_notes, note: note
+        = render "projects/notes/discussion_diff", discussion_notes: discussion_notes, note: note
       - else
         = link_to 'show outdated discussion', '#', class: 'js-show-outdated-discussion'
         %div.hide.outdated-discussion
-          .content
           .notes{ rel: discussion_notes.first.discussion_id }
             = render discussion_notes
 
-
     - else
-      .content
       .notes{ rel: discussion_notes.first.discussion_id }
         = render discussion_notes
       = render "projects/notes/discussion_reply_button", note: discussion_notes.first
@@ -59,4 +55,3 @@
         = link_to "javascript:;", class: "js-details-target js-toggler-target" do
           %i.icon-eye-open
           Show
-

app/views/projects/notes/_discussion_diff.html.haml

 - diff = note.diff
-.header
+.diff-file
+  .diff-header
     - if diff.deleted_file
       %span= diff.old_path
     - else
@@ -7,7 +8,7 @@
       - if diff.a_mode && diff.b_mode && diff.a_mode != diff.b_mode
         %span.file-mode= "#{diff.a_mode} → #{diff.b_mode}"
     %br/
-.content
+  .diff-content
     %table
       - each_diff_line_near(diff, note.diff_file_index, note.line_code) do |line, type, line_code, line_new, line_old|
         %tr.line_holder{ id: line_code }