Remove NioNotEnabledBootstrapCheck bootstrap check (#28901)

This is related to #27260. This commit removes the bootstrap check that
prevents nio from being enabled.

plugins/transport-nio/src/main/java/org/elasticsearch/transport/nio/NioNotEnabledBootstrapCheck.java

@@ -1,32 +0,0 @@
-/*
- * Licensed to Elasticsearch under one or more contributor
- * license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright
- * ownership. Elasticsearch licenses this file to you under
- * the Apache License, Version 2.0 (the "License"); you may
- * not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-package org.elasticsearch.transport.nio;
-
-import org.elasticsearch.bootstrap.BootstrapCheck;
-import org.elasticsearch.bootstrap.BootstrapContext;
-
-public class NioNotEnabledBootstrapCheck implements BootstrapCheck {
-
-    @Override
-    public BootstrapCheckResult check(BootstrapContext context) {
-        return BootstrapCheckResult.failure("The transport-nio plugin is experimental and not ready for production usage. It should " +
-            "not be enabled in production.");
-    }
-}

plugins/transport-nio/src/main/java/org/elasticsearch/transport/nio/NioTransportPlugin.java

@@ -61,9 +61,4 @@ public class NioTransportPlugin extends Plugin implements NetworkPlugin {
             () -> new NioTransport(settings, threadPool, networkService, bigArrays, pageCacheRecycler, namedWriteableRegistry,
                 circuitBreakerService));
     }
-
-    @Override
-    public List<BootstrapCheck> getBootstrapChecks() {
-        return Collections.singletonList(new NioNotEnabledBootstrapCheck());
-    }
 }