Nginx - do not log media files requests

For some historical reasons, some requests to media or other download-type files were logged in the Nginx access log. However, after introducing pseudo-streaming server-side support for H.264/AAC files, this may cause floods in the access logs due to the way the pseudo-streaming works, which in turn may trigger DoS protection (like used in BOA) and block the remote IP address temporarily. We should remove this logging to avoid such false positives.