Remove attempt to use index.html other than as a fallback

If we have index.html in try_files, requests for files that should result in 404 somehow work into the same redirect loop that is described in http://core.trac.wordpress.org/ticket/20746

By leaving the other index.html line in the config, it is still used as the default fallback, there is just no need to use try_files in combo with it.

See #233