[6.x] Fix Builder::withCount() binding error when a scope is added into related model with binding in a sub-select

[miklcct]

In current Laravel, Builder::withCount() causes an error if the related model has a scope which adds a sub-select with bindings, for example, the following scope attempts to add a column called "liked" into Likeable models, but causes an error when a model with it is loaded in Builder::withCount().

class LikeScope implements Scope
{
    public function apply(Builder $builder, Model $model)
    {
        if ($model instanceof Likeable) {
            if ($builder->getQuery()->columns === null) {
                $builder->select(['*']);
            }
            $builder->selectSub(
                Like::whereColumn('likeable_id', '=', $model->getTable() . '.id')->whereLikeableType($model->getMorphClass())->whereUserId(
                    app(User::class)->id
                )
                    ->selectRaw('count(*)')
                ,
                'liked'
            );
        }
    }
}

It's because Builder::withCount() removes extra columns added by the scope when loading the count, but forgets to remove the extra "select" bindings added.

This one-line patch fixes the problem.