fix #2110

This is a possible fix for issue #2110 (closed).

The following issue(s) remain:

I dont get why help.cfg has to be initialized by default. Without executing further aliases or using server hooks it does nothing...

Instead https://gitlab.com/xonotic/xonotic/blob/master/server/server.cfg should just contain exec help.cfg as follows:

// TIPS: uncomment this if you want help messages on your server - one per match 20 seconds after the map loads
//exec help.cfg
//alias sv_hook_gamestart_all "defer 20 help_next"

Using the sv_hook_gamestart alias is probably not the best solution. I don't think people want to read help messages when the match started. I guess sv_hook_gameend is a better option. I don't know if it collides with existing aliases.