Reduce field size down to 255 utf8 characters

MySQL count 3 bytes per UTF8 character which makes the index go too large

Remove indexation of appli field which is too wide for MySQL
Remove use of appli index as was deleted

lib/classes/module/report/nav.php

@@ -351,7 +351,7 @@ class module_report_nav extends module_report
 
         $sql = '
             SELECT appli
-                FROM log FORCE INDEX (date_site, appli)
+                FROM log FORCE INDEX (date_site)
                 WHERE ' . $report_filter['sql'] . ' AND appli != \'a:0:{}\' AND !ISNULL(usrid)
             GROUP BY appli';