docs: remove stale OpenVoxDB CONTRIBUTING page

The OpenVoxDB collection carried a published "Contributing to OpenVoxDB"
page mirrored from PuppetDB's docs. It was stale Puppet-era boilerplate
(freenode #puppet-dev, Puppet Jira, the Puppet CLA) and duplicated
governance that already has a canonical home in the org-level
OpenVoxProject/.github CONTRIBUTING guide.

- Delete docs/_openvoxdb_8x/CONTRIBUTING.md and its nav entry
- Delete the unused legacy _puppetdb_nav.html (also linked to it)
- Repoint install_from_source.markdown's "run tests locally" link to
  the upstream dev-docs/local-dev.md, the current home for OpenVoxDB
  development and test-setup instructions

Closes #247

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Michael Harp <mike@mikeharp.com>

Author: miharp

_data/nav/openvoxdb_8x.yml

@@ -5,8 +5,6 @@
     link: release_notes.html
   - text: Overview and requirements
     link: index.html
-  - text: Contributing to OpenVoxDB
-    link: CONTRIBUTING.html
   - text: Frequently asked questions
     link: puppetdb-faq.html
   - text: Versioning policy