code: public function remove($item, $quantity = 0)
      {
          // Get item
          $cartItem = $this->getItem(is_array($item) ? $item['sku'] : $item->sku);
          // Remove or decrease quantity
          if (!empty($cartItem)) {
              if (!empty($quantity)) {
                  $cartItem->quantity -= $quantity;
                  $cartItem->save();
                  if ($cartItem->quantity > 0) return true;
              }
              $cartItem->delete();
          }
          $this->resetCalculations();
          return $this;
      }
docs: Removes an item from the cart or decreases its quantity.
  Returns flag indicating if removal was successful.
  
  @param mixed $item     Item to remove, can be an Store Item, a Model with ShopItemTrait or an array.
  @param int   $quantity Item quantity to decrease. 0 if wanted item to be removed completly.
  
  @return bool