chore: delete stale branch action | NPG-000 (#736)

# Description

Stops old branches from being purged.

This repo doesn't see much updates anymore.
We may need to keep a branch for a long time, with a patch or
experimental change.
This update just removes the stake branches cleanup task, to prevent
them from being purged.

## Type of change

Please delete options that are not relevant.

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update

## Checklist

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [x] Any dependent changes have been merged and published in downstream
modules

Author: stevenj