man-pages.scss: drop listingblock formatting
man-pages.scss: drop listingblock formatting

The content is all inside a <pre> block, which already gets the same
formatting via our rule in application.scss. The result with the
duplication looks bad, with an extra bit of empty bordered content
before and after each block.

Mokolea/git-scm.com,git/git-scm.com,Mokolea/git-scm.com,mosoft521/gitscm-next,Mokolea/git-scm.com,Mokolea/git-scm.com,git/git-scm.com,mosoft521/gitscm-next,git/git-scm.com,git/git-scm.com,mosoft521/gitscm-next,mosoft521/gitscm-next