Remove language_css_alter() (RTL stylesheets) in favor of HTML 'dir' attribute.

pr for: https://github.com/backdrop/backdrop-issues/issues/207
For some reason the .rej files appear in all branches not just the one I was working on. Any idea why that would be?
We don't need to add the \@file docblock here, and these selectors should be next to the matching rules.