Remove SearchableSnapshotIndexMetadataUpgrader (elastic#114290)

This service only exists to fix up the metadata on 7.x searchable
snapshot indices during/after an upgrade to 8.x, so we don't need it in
9.x.

Author: DaveCTurner

x-pack/plugin/searchable-snapshots/src/main/java/org/elasticsearch/xpack/searchablesnapshots/SearchableSnapshots.java

@@ -108,7 +108,6 @@
 import org.elasticsearch.xpack.searchablesnapshots.rest.RestSearchableSnapshotsNodeCachesStatsAction;
 import org.elasticsearch.xpack.searchablesnapshots.rest.RestSearchableSnapshotsStatsAction;
 import org.elasticsearch.xpack.searchablesnapshots.store.SearchableSnapshotDirectory;
-import org.elasticsearch.xpack.searchablesnapshots.upgrade.SearchableSnapshotIndexMetadataUpgrader;
 
 import java.io.IOException;
 import java.io.UncheckedIOException;
@@ -359,7 +358,6 @@ public Collection<?> createComponents(PluginServices services) {
         components.add(new FrozenCacheServiceSupplier(frozenCacheService.get()));
         components.add(new CacheServiceSupplier(cacheService.get()));
         if (DiscoveryNode.isMasterNode(settings)) {
-            new SearchableSnapshotIndexMetadataUpgrader(clusterService, threadPool).initialize();
             clusterService.addListener(new RepositoryUuidWatcher(services.rerouteService()));
         }
         return Collections.unmodifiableList(components);