Removed dark and alt links

Removed the link rot for dark and alt themes as they are invalid.

Author: ardahal

README.md

@@ -1,8 +1,6 @@
 # Markdown css theme collection
 
 * [Light](http://jasonm23.github.com/markdown-css-themes/index.html)
-* [Dark](http://jasonm23.github.com/markdown-css-themes/dark.html)
-* [Alt](http://jasonm23.github.com/markdown-css-themes/alt.html)
 * [Foghorn](http://jasonm23.github.com/markdown-css-themes/foghorn.html)
 * [Swiss](http://jasonm23.github.com/markdown-css-themes/swiss.html)