DEV: Use guardian user for can_chat? (#19418)

Instead of passing `user` to `guardian.can_chat?`, we
can just use the inner `@user` that is part of the guardian
instance already to determine whether that user can chat,
since this is how it works for all other usages of guardian
even within chat.

plugins/chat/lib/guardian_extensions.rb

@@ -10,10 +10,9 @@ module Chat::GuardianExtensions
     end
   end
 
-  def can_chat?(user)
-    return false unless user
-
-    user.staff? || user.in_any_groups?(Chat.allowed_group_ids)
+  def can_chat?
+    return false if anonymous?
+    @user.staff? || @user.in_any_groups?(Chat.allowed_group_ids)
   end
 
   def can_create_chat_message?