Remove diff summary from document history sidebar.

Cause of occassional memory leaks and downtime :(

server/api/documents.js

@@ -231,9 +231,7 @@ router.post('documents.revisions', auth(), pagination(), async ctx => {
   });
 
   const data = await Promise.all(
-    revisions.map((revision, index) =>
-      presentRevision(ctx, revision, revisions[index + 1])
-    )
+    revisions.map((revision, index) => presentRevision(ctx, revision))
   );
 
   ctx.body = {

server/presenters/revision.js

@@ -1,25 +1,8 @@
 // @flow
-import * as JSDiff from 'diff';
 import { Revision } from '../models';
 import presentUser from './user';
 
-function counts(changes) {
-  return changes.reduce(
-    (acc, change) => {
-      if (change.added) acc.added += change.value.length;
-      if (change.removed) acc.removed += change.value.length;
-      return acc;
-    },
-    {
-      added: 0,
-      removed: 0,
-    }
-  );
-}
-
-function present(ctx: Object, revision: Revision, previous?: Revision) {
-  const prev = previous ? previous.text : '';
-
+function present(ctx: Object, revision: Revision) {
   return {
     id: revision.id,
     documentId: revision.documentId,
@@ -27,7 +10,6 @@ function present(ctx: Object, revision: Revision, previous?: Revision) {
     text: revision.text,
     createdAt: revision.createdAt,
     createdBy: presentUser(ctx, revision.user),
-    diff: counts(JSDiff.diffChars(prev, revision.text)),
   };
 }