batch.remove() now removes from db.keydir

was trying out the new batches for use in medeadown, but was bitten by this
Can you add some curly brackets around this block?

```js
if (operation.type === 'remove') {
  // ...
} else {
  // ...
}
```
I have seen a lack of curly brackets lead to developers introducing bugs (across multiple programming languages), so I try to make it a good practice to always include them.  Just a style nitpick.  Other than that, this PR looks good!