remove adjustments finalize!

According to commit 953c960680f284a2eb97b160a4610a72494ce107. 
This commit removes the confusing "finalized" state  from Spree::Adjustment.

When I click ship button in admin, it will throw error in after_ship method since no finalize! method in adjustment any more.
```
undefined method `finalize!' for #<Spree::Adjustment:0x000001095a1180>
```