(OG) Remove express serve-static middleware

Co tenhle MR dělá? / What does this MR do?

Changed

• Stop serving /.well-known/security.txt

Removed

• Remove Express serve-static middleware (vp/og#1)

Související issues / Related issues

https://gitlab.com/operator-ict/golemio/code/vp/output-gateway/-/issues/1

Vývojářův kontrolní seznam / Developer checklist

• Ensure this change works
• Write unit tests for this change as needed
• Update the OpenAPI document if exists
• Ensure CI/CD pipeline passes
• Create or update the implementation documentation if necessary
• Include a changelog entry
• Request a review

Recenzentův kontrolní seznam / Reviewer checklist

• Ensure this change follows CODING-GUIDELINES and CONTRIBUTING
• Ensure this change follows the Golemio/OICT architecture
• Ensure this change does not add unnecessary dependencies (e.g. lodash)
• The changelog is updated
• The implementation documentation is created or updated if necessary
• The OpenAPI document is updated if exists