Remove @UpdateForV10 annotation in 8.x (elastic#125084)

The `8.x` branch doesn't know anything about v10-only changes.
Backporting code from 9.x to 8.x branches doesn't work anyway if it
mentions `@UpdateForV10`. This commit just removes the `@UpdateForV10`
annotation entirely in the `8.x` branch.

Author: DaveCTurner

libs/core/src/main/java/org/elasticsearch/core/UpdateForV10.java

@@ -115,7 +115,6 @@ private static IntFunction<String> lookupFunction(NavigableMap<Integer, List<Ver
                     // maybe keep the release mapping around in the csv file?
                     // SEP for now
                     @UpdateForV9
-                    // @UpdateForV10
                     Version oldVersion = Version.fromId(id);
                     return oldVersion.toString();
                 }

server/src/main/java/org/elasticsearch/ReleaseVersions.java

@@ -28,7 +28,6 @@
 import java.util.List;
 
 @UpdateForV9
-// @UpdateForV10 // this can be removed in v10. It may be called by v8 nodes to v9 nodes.
 public class TransportNodesFeaturesAction extends TransportNodesAction<
     NodesFeaturesRequest,
     NodesFeaturesResponse,

server/src/main/java/org/elasticsearch/action/admin/cluster/node/features/TransportNodesFeaturesAction.java

@@ -1,5 +1,4 @@
 [
   "Content moved to reference-docs-links.txt",
-  "This is a temporary placeholder to satisfy sub check_elasticsearch_links in the docs build",
-  "Remove with @UpdateForV10 (if not before)"
+  "This is a temporary placeholder to satisfy sub check_elasticsearch_links in the docs build"
 ]