chore(source-notion): Remove stale OpenAPI spec URL from external documentation (#70446)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Christo Grabowski <christo.grabowski@airbyte.io>

airbyte-integrations/connectors/source-notion/metadata.yaml

@@ -20,9 +20,6 @@ data:
     - title: Changelog
       url: https://developers.notion.com/page/changelog
       type: api_release_history
-    - title: Notion API OpenAPI specification
-      url: https://github.com/ramnes/notion-sdk-py/blob/main/notion_client/openapi.json
-      type: openapi_spec
   githubIssueLabel: source-notion
   icon: notion.svg
   license: ELv2