[chore] Remove no longer needed front matter properties (#2972)

Author: thompson-tomo

CONTRIBUTING.md

@@ -198,9 +198,6 @@ headers like the following:
 ```md
 <!--- Hugo front matter used to generate the website version of this page:
 linkTitle: HTTP
-path_base_for_github_subdir:
-  from: content/en/docs/specs/semconv/http/_index.md
-  to: http/README.md
 --->
 ```