Remove store-specific rules from DiscountApplied

Removed rule for 10% and 15% discounts, see issue #340
elseif ($strl == 15 && $CORE_LOCAL->get("isStaff") == 0 && 
(substr($CORE_LOCAL->get("memberID"), 0, 1) != "9" ||
 strlen($CORE_LOCAL->get("memberID")) != 6)
) 
    $this->ret['output'] = DisplayLib::boxMsg(_("Staff discount not applicable"));
elseif ($strl == 10 && $CORE_LOCAL->get("isMember") == 0) 
    $this->ret['output'] = DisplayLib::boxMsg(_("Member discount not applicable"));