Merge pull request #4604 from reasonerjt/custom-plugin-doc-update-1.8

[Cherry pick to 1.8] Undeprecate the volumesnapshot plugin in the doc

site/content/docs/main/custom-plugins.md

@@ -54,14 +54,10 @@ You will need to give your plugin(s) the full name when registering them by call
 Velero supports the following kinds of plugins:
 
 - **Object Store** - persists and retrieves backups, backup logs and restore logs
-- **Item Snapshotter** - creates snapshots for Kubernetes objects during backup and restores the object from snapshots during restore.  ItemSnapshotters
-  are typically used with the [Astrolabe](https://github.com/vmware-tanzu/astrolabe) framework.
+- **Volume Snapshotter** - creates volume snapshots (during backup) and restores volumes from snapshots (during restore)
 - **Backup Item Action** - executes arbitrary logic for individual items prior to storing them in a backup file
 - **Restore Item Action** - executes arbitrary logic for individual items prior to restoring them into a cluster
 - **Delete Item Action** - executes arbitrary logic based on individual items within a backup prior to deleting the backup
-## Deprecated plugin kinds
-- **Volume Snapshotter** - creates volume snapshots (during backup) and restores volumes from snapshots (during restore)  VolumeSnapshotters
-are deprecated and will be replaced with ItemSnapshotter/Astrolabe plugins.
 
 ## Plugin Logging