MvxCollectionViewSourceAnimated bug while using MvxObservableCollection.RemoveItems
## 🐛 Bug Report

This bug is reproducing on **iOS** platform, while using `MvxCollectionViewSourceAnimated` with binding to an `MvxObservableCollection`.
While modifying the `MvxObservableCollection` using `RemoveItems` or `SwitchTo` methods the `UICollectionView` gets broken displaying a wrong number of items.

NOTE: It doesn't happen with `MvxCollectionViewSource`.

### Expected behavior

`UICollectionView` should display a correct number of items after `MvxObservableCollection.RemoveItems` usage.

### Reproduction steps

1) Create an `UICollectionView` and attach `MvxCollectionViewSourceAnimated` to it
2) Create a view model, add `MvxObservableCollection Items` property, and bind the property to the `MvxCollectionViewSourceAnimated`
3) Use `MvxObservableCollection.RemoveItems` to remove some items from the observable collection and observe the `UICollectionView` behaviour

There is also a log in the output:
```
[UICollectionView] Invalid update: invalid number of items in section 0.  The number of items contained in an existing section after the update (4) must be equal to the number of items contained in that section before the update (6), plus or minus the number of items inserted or deleted from that section (0 inserted, 0 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out). - will perform reloadData.
```

I've create a sample **Xamarin.ios** application to test this issue: https://github.com/DmitriyKirakosyan/TestAnimatedCollection

### Configuration

**Version:** 6.x

**Platform:** 
- [x] :iphone: iOS
- [ ] :robot: Android
- [ ] :checkered_flag: WPF
- [ ] :earth_americas: UWP
- [ ] :apple: MacOS
- [ ] :tv: tvOS
- [ ] :monkey: Xamarin.Forms
