fix clean param

Author: Melevir

landing_page/mainpage/static/robots.txt

@@ -3,4 +3,4 @@ Disallow: /admin/
 Disallow: /success/
 Disallow: /lessons/
 Sitemap: http://learn.python.ru/sitemap.xml
-Clean-param: utm ref source trk 1* 2* 3* 4* 5* 6* 7* 8* 9*
+Clean-param: utm ref source trk