doc: fix scaleway_ip_reverse_dns v2 migration guide (#514)

Author: jerome-quere

website/docs/guides/migration_guide_v2.html.markdown

@@ -136,17 +136,9 @@ The `scaleway_token` was removed in version 2.
 
 Tokens should be created in the console.
 
-#### Removed: `scaleway_ip_reverse_dns`
+#### Renamed: `scaleway_ip_reverse_dns` -> `scaleway_instance_ip_reverse_dns`
 
-The `scaleway_ip_reverse_dns` was removed in version 2.
-
-Reverse DNS must be set on the IP resource itself:
-
-```hcl
-resource "scaleway_instance_ip" "test_ip" {
-  reverse = "scaleway.com"
-}
-```
+`scaleway_ip_reverse_dns` was renamed to `scaleway_instance_ip_reverse_dns`.
 
 #### Removed: `scaleway_volume_attachment`