[improve] remove demo plugin (#2492)

Co-authored-by: tomsun28 <tomsun28@outlook.com>

plugin/src/main/java/org/apache/hertzbeat/plugin/impl/DemoPluginImpl.java

@@ -1,40 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF 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.apache.hertzbeat.plugin.impl;
-
-import lombok.extern.slf4j.Slf4j;
-import org.apache.hertzbeat.common.entity.alerter.Alert;
-import org.apache.hertzbeat.plugin.Plugin;
-
-/**
- * DemoPlugin
- */
-@Slf4j
-public class DemoPluginImpl implements Plugin {
-
-    /**
-     * execute when alert
-     */
-    @Override
-    public void alert(Alert alert) {
-        if (log.isDebugEnabled()) {
-            log.debug("DemoPluginImpl alert: {}", alert);   
-        }
-    }
-
-}

plugin/src/main/resources/META-INF/services/org.apache.hertzbeat.plugin.Plugin

@@ -1 +0,0 @@
-org.apache.hertzbeat.plugin.impl.DemoPluginImpl