chore: remove kramdown

[thompson-tomo]

Remove kramdown from sem conv gem which appears not to be used.

Also The docs appear to not be published as link points to a url which lacks a link to sem-conv.

[kaylareopelle]

The kramdown removal looks good to me.

Also The docs appear to not be published as link points to a url which lacks a link to sem-conv.

I can find the docs on rubydoc: https://rubydoc.info/gems/opentelemetry-semantic_conventions

Should the link that you're referring to be somewhere on this page? https://open-telemetry.github.io/opentelemetry-ruby/

[thompson-tomo]

@kaylareopelle according to the gemspec the documentation is at https://open-telemetry.github.io/opentelemetry-ruby/opentelemetry-semantic_conventions/v#{OpenTelemetry::SemanticConventions::VERSION which redirects to https://open-telemetry.github.io/opentelemetry-ruby/ and semantic conventions is not listed.

Let's update the links seperately.

[thompson-tomo]

Links have been addressed in #2123