Percentage payment surcharge is calculated wrong

[svenmuennich]

When configuring the shop to charge no VAT and having a payment method with a percentage surcharge, the respective surcharge position in the basket contains VAT. This is caused by adding a wrong surcharge position in sBasket::sInsertSurchargePercent(), although a correct position was already added by sAdmin::handlePaymentMeanSurcharge().

To me sBasket::sInsertSurchargePercent() seems obsolete, since it only calculates percentage payment method discounts. So removing this method might just fix it.