[NO GBP] Fix channel announcements not working with multiple values (…

…#89524)

forgot to remove the defaults, with those the configs get interpreted as
one big string instead of a list

code/controllers/configuration/entries/general.dm

@@ -583,13 +583,10 @@
 	return "" //default broadcast
 
 /datum/config_entry/str_list/channel_announce_new_game
-	default = null
 
 /datum/config_entry/str_list/channel_announce_end_game
-	default = null
 
 /datum/config_entry/str_list/chat_new_game_notifications
-	default = null
 
 /// validate ownership of admin flags for chat commands
 /datum/config_entry/flag/secure_chat_commands