[azure] Revert discovery plugins must declare their UnicastHostsProvider

Related to #13492

The previous fix is not working for Azure Plugin.
I will work on a new fix for it but for now, I'm reverting the change for azure.

plugins/cloud-azure/src/main/java/org/elasticsearch/plugin/cloud/azure/CloudAzurePlugin.java

@@ -26,7 +26,6 @@ import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.DiscoveryModule;
 import org.elasticsearch.discovery.azure.AzureDiscovery;
-import org.elasticsearch.discovery.azure.AzureUnicastHostsProvider;
 import org.elasticsearch.index.snapshots.blobstore.BlobStoreIndexShardRepository;
 import org.elasticsearch.index.store.IndexStoreModule;
 import org.elasticsearch.index.store.smbmmapfs.SmbMmapFsIndexStore;
@@ -81,7 +80,6 @@ public class CloudAzurePlugin extends Plugin {
 
     public void onModule(DiscoveryModule discoveryModule) {
         discoveryModule.addDiscoveryType("azure", AzureDiscovery.class);
-        discoveryModule.addUnicastHostProvider(AzureUnicastHostsProvider.class);
     }
 
     public void onModule(IndexStoreModule storeModule) {