doc: fix release process table of contents

The table of contents for the release process still references a
deleted section. Remove that reference, and renumber the following
table of contents entries so that they link through to the correct
sections.

PR-URL: #50216
Refs: #45858
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>

Author: richardlau

doc/contributing/releases.md

@@ -32,9 +32,8 @@ official release builds for Node.js, hosted on <https://nodejs.org/>.
   * [16. Check the release](#16-check-the-release)
   * [17. Create a blog post](#17-create-a-blog-post)
   * [18. Create the release on GitHub](#18-create-the-release-on-github)
-  * [19. Cleanup](#19-cleanup)
-  * [20. Announce](#20-announce)
-  * [21. Celebrate](#21-celebrate)
+  * [19. Announce](#19-announce)
+  * [20. Celebrate](#20-celebrate)
 * [LTS releases](#lts-releases)
 * [Major releases](#major-releases)