Remove line-height override CSS github.com/shurcooL/issuesapp#27

Setting the line-height to initial makes spacing content elements within threads inconsistent with the rest of sourcegraph. Remove this global style and set it only on the element that need it (list-entry-header etc.)

Go for it (as we discussed), but it's likely that "only the element that need it" = almost all elements except a few that display user content/comment body.

I want to refactor and improve CSS and frontend rendering in general for this project down the line. This specific task isn't really relevant anymore, closing since it's unhelpful to track it individually.