docs: remove release instructions for release branch (#6097)

The branch called `release` is an old branch created when we had Grafana
Cloud install scripts and needed to update it dynamically.

This branch has not been used, and there are no remaining references to
it, so we can remove the branch and remove the instructions to update
it.

docs/developer/release/README.md

@@ -8,13 +8,13 @@ The processes described here are for v0.24.0 and above.
 
 # Release Cycle
 
-A typical release cycle is to have a Release Candidate published for at least 48 
+A typical release cycle is to have a Release Candidate published for at least 48
 hours followed by a Stable Release. 0 or more Patch Releases may occur between the Stable Release
 and the creation of the next Release Candidate.
 
 # Workflows
 
-Once a release is scheduled, a release shepherd is determined. This person will be 
+Once a release is scheduled, a release shepherd is determined. This person will be
 responsible for ownership of the following workflows:
 
 ## Release Candidate Publish
@@ -39,20 +39,18 @@ responsible for ownership of the following workflows:
 2. [Update Version in Code](./3-update-version-in-code.md)
 3. [Tag Release](./4-tag-release.md)
 4. [Publish Release](./6-publish-release.md)
-5. [Update Release Branch](./5-update-release-branch.md)
-6. [Test Release](./7-test-release.md)
-7. [Update Helm Charts](./8-update-helm-charts.md)
-8. [Announce Release](./9-announce-release.md)
-9. [Update OTEL Contrib](./10-update-otel.md)
+5. [Test Release](./7-test-release.md)
+6. [Update Helm Charts](./8-update-helm-charts.md)
+7. [Announce Release](./9-announce-release.md)
+8. [Update OTEL Contrib](./10-update-otel.md)
 
 ## Patch Release Publish (latest version)
 1. [Cherry Pick Commits](./2-cherry-pick-commits.md)
 2. [Update Version in Code](./3-update-version-in-code.md)
 3. [Tag Release](./4-tag-release.md)
 4. [Publish Release](./6-publish-release.md)
-5. [Update Release Branch](./5-update-release-branch.md) 
-6. [Update Helm Charts](./8-update-helm-charts.md)
-7. [Announce Release](./9-announce-release.md)
+5. [Update Helm Charts](./8-update-helm-charts.md)
+6. [Announce Release](./9-announce-release.md)
 
 ## Patch Release Publish (older version)
 - Not documented yet (but here are some hints)
@@ -61,6 +59,5 @@ responsible for ownership of the following workflows:
   - cherry-pick commit[s] into it
   - don't update the version in the project on main
   - changes go into the changelog under the patch release version plus stay in unreleased
-  - don't update the `release` branch
   - don't publish in github as latest release
   - don't update deployment tools or helm charts