Revert "content [nfc]: Add comments linking to CZO, pending API-doc update"

This reverts commit 5515ab9.

Author: MritunjayTiwari14

lib/model/content.dart

@@ -1417,14 +1417,9 @@ class _ZulipContentParser {
       thumbnailUrl = src;
     } else if (src.startsWith('/external_content/')
         || src.startsWith('https://uploads.zulipusercontent.net/')) {
-      // This image preview uses camo, which still happens on current servers
-      // (2025-10); discussion:
-      //   https://chat.zulip.org/#narrow/channel/412-api-documentation/topic/documenting.20inline.20images/near/2279235
       srcUrl = src;
       thumbnailUrl = null;
     } else if (href == src)  {
-      // Probably generated by a server before the thumbnailing feature landed:
-      //   https://chat.zulip.org/#narrow/channel/412-api-documentation/topic/documenting.20inline.20images/near/2279234
       srcUrl = src;
       thumbnailUrl = null;
     } else {