Fix up some notes tech debt

Fix up tech debt comments from @jschatz1

 - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10837#note_28757436
 - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10837#note_28757905
 - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10837#note_28757952
 - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10837#note_28758013

spec/javascripts/notes_spec.js

@@ -128,7 +128,6 @@ import '~/notes';
       beforeEach(() => {
         note = {
           id: 1,
-          discussion_html: null,
           valid: true,
           note: 'heya',
           html: '<div>heya</div>',