Remove unused code
Remove unused code

The class of pre element was a legacy behavior. The Rouge formatter (ouge::Formatters::HTMLLegacy) used to wrap the highlight inside a `div`. The current formatter (`Rouge::Formatters::HTML`) we’re using does not do this any more.

Also confirm with the code blocks behavior from Commonmark spec[1] and GitHub flavored spec[2] do not add class attribute to pre element.

Hence the node here does not have class to set here.

[1] https://spec.commonmark.org/0.29/#fenced-code-blocks
[2] https://github.github.com/gfm/#fenced-code-blocks

jch/html-pipeline,jch/html-pipeline,gjtorikian/html-pipeline,gjtorikian/html-pipeline