roles/nginx: Remove Internet Explorer 6 gzip disable

I have zero idea if we have IE6 clients any more, but according to the
H5BP community IE6 actually did support gzip and only represents 0.1%
of Internet traffic in 2015 (!) anyways.

See: https://github.com/h5bp/server-configs-nginx/issues/125

roles/nginx/templates/nginx.conf.j2

@@ -68,7 +68,6 @@ http {
     # larger files after gzipping).
     gzip_min_length 256;
 
-    gzip_disable "msie6";
     gzip_http_version 1.1;
     # Compress all output labeled with one of the following MIME-types.
     gzip_types