Drop item adjustments update call

Currently the line item adjustments are already updated when / if a
tax adjustment is created via line item save callback which in turn
triggers an adjustment save callback that calls ItemAdjustments#update

The same code will also be executed during `recalculate_adjustments`
which will update / recalculate ALL order adjustments (including the
ones linked to line items). Our build doesn't have any example to
support these recalculations being called in all these places

ItemAdjustments update on the order was also changed to only run once