doc: remove outstanding YAML comment

Refs: https://github.com/nodejs/remark-preset-lint-node/pull/139

PR-URL: https://github.com/nodejs/node/pull/35454
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ujjwal Sharma <ryzokuken@disroot.org>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Michael Dawson <midawson@redhat.com>

doc/api/buffer.md

@@ -776,10 +776,6 @@ This is the size (in bytes) of pre-allocated internal `Buffer` instances used
 for pooling. This value may be modified.
 
 ### `buf[index]`
-<!-- YAML
-type: property
-name: [index]
--->
 
 * `index` {integer}