[docs] remove registerPolicies call that was removed with L10.0.2

The line was previously there just to be a goalpost, to give an idea where to put the suggested new code.

docs/basic-usage/super-admin.md

@@ -18,7 +18,7 @@ class AuthServiceProvider extends ServiceProvider
 {
     public function boot()
     {
-        $this->registerPolicies();
+//...
 
         // Implicitly grant "Super Admin" role all permissions
         // This works in the app by using gate-related functions like auth()->user->can() and @can()