remove old posts

docs/notifications.json

@@ -9,11 +9,6 @@
     "id": 53,
     "text": "You can <a style=\"color: inherit;\" target=\"_blank\" rel=\"noopener\" href=\"https://twitter.com/MUI_hq\">follow us on Twitter</a> to receive exclusive tips and updates about MUI and the React ecosystem."
   },
-  {
-    "id": 62,
-    "title": "🗓 <b>MUI X expands its product line with advanced date and time picker components</b>",
-    "text": "<a style=\"color: inherit;\" data-ga-event-category=\"Blog\" data-ga-event-action=\"notification\" data-ga-event-label=\"lab-date-pickers-to-mui-x/\" href=\"/blog/lab-date-pickers-to-mui-x/\">Check out the blog post</a> to learn how to migrate to the new package and start building with our powerful date and time pickers, now part of MUI X."
-  },
   {
     "id": 63,
     "title": "📄 <b>Our docs just got a major upgrade!</b>",