docs(release): update instructions after introducing Towncrier (#1304)

Removes old instructions that don't apply after intruduction of Towncrier.

docs/release.md

@@ -5,7 +5,6 @@
   - [Create and push Git tag](#create-and-push-git-tag)
     - [Remove tag in case of a failed release job](#remove-tag-in-case-of-a-failed-release-job)
   - [Publish GitHub release](#publish-github-release)
-  - [Add `Unreleased` section to the changelog and upgrading guide](#add-unreleased-section-to-the-changelog-and-upgrading-guide)
   - [Build packages](#build-packages)
 - [Updating OT to next version](#updating-ot-to-next-version)
   - [Update OT version](#update-ot-version)
@@ -24,8 +23,6 @@ Update the [CHANGELOG.md][changelog] by running `make update-changelog VERSION=x
 
 Make sure the [upgrading.md][upgrading] file has entries for the breaking changes for this release.
 
-Here are some example pull requests: [#602], [#652], [#684].
-
 ### Create and push Git tag
 
 In order to release a new version of Sumo OT distro you'd export `TAG` env variable
@@ -80,14 +77,6 @@ edit the release draft and fill in missing information:
 
 After verifying that the release text and all links are good, publish the release.
 
-### Add `Unreleased` section to the changelog and upgrading guide
-
-Edit the [CHANGELOG.md][changelog] and [upgrading.md][upgrading] files and prepare unreleased section.
-
-Here is the example pull request: [#677].
-
-[#677]: https://github.com/SumoLogic/sumologic-otel-collector/pull/677
-
 ### Build packages
 
 1. Open the [Build packages workflow][build_packages_workflow] in GitHub Actions for the