Remove getPosition()

The original idea of including this function in `./view.js` seems to be
that it's shared between the demo reader and Foliate. But

- It's currently not used in the demo reader any more.
- It works, but it lacks features.
- In any case it's not coupled with anything else in `./view.js`, so at
  best it should be a separate module.

Also: remove unused variable and fix indentation

reader.js

@@ -1,4 +1,4 @@
-import { View, getPosition } from './view.js'
+import { View } from './view.js'
 import { createTOCView } from './ui/tree.js'
 import { createMenu } from './ui/menu.js'