fp-completely class is not applied to sections when navigated to via Drag and Move

### Description
The fp-completely class isn't properly applied to the new section or removed from the previous when navigating to the next section via the Drag and Move gesture.

### Link to isolated reproduction with no external CSS / JS
https://alvarotrigo.com/fullPage/extensions/drag-and-move.html

### Steps to reproduce it
1. Inspect the div.section elements
2. Navigate to a new section via Drag and Move gesture

### Versions
MacOS 10.15.5, Google Chrome 83.0.4103.116