Issue Description

Type: bug report or feature request

Describe what happened (or what feature you want)

网关流控API
当我添加一个API 定义之后，会同时更新GatewayApiMatcherManager
但是当我再将这个API 定义删除之后，也会更新GatewayApiMatcherManager，不过它只会添加不会删除。
具体代码如下：

static synchronized void loadApiDefinitions(/*@Valid*/ Set<ApiDefinition> definitions) {
        if (definitions == null || definitions.isEmpty()) {
            API_MATCHER_MAP.clear();
            return;
        }
        definitions.forEach(GatewayApiMatcherManager::addApiDefinition);
    }

我做了一些小的修改，就可以处理这个问题了。

// 去除final 修饰
    // private static final Map<String, WebExchangeApiMatcher> API_MATCHER_MAP = new ConcurrentHashMap<>();
    private static Map<String, WebExchangeApiMatcher> API_MATCHER_MAP = new ConcurrentHashMap<>();

// 修改loadApiDefinitions() 方法的逻辑
    static synchronized void loadApiDefinitions(/*@Valid*/ Set<ApiDefinition> definitions) {
        Map<String, WebExchangeApiMatcher> apiMatcherMap = new ConcurrentHashMap<>();
        for (ApiDefinition definition : definitions) {
            apiMatcherMap.put(definition.getApiName(), new WebExchangeApiMatcher(definition));
        }
        API_MATCHER_MAP = apiMatcherMap;
    }

Describe what you expected to happen

How to reproduce it (as minimally and precisely as possible)

Tell us your environment

我这边使用的依赖包以及版本

<dependency>
	<groupId>com.alibaba.csp</groupId>
	<artifactId>sentinel-spring-cloud-gateway-adapter</artifactId>
	<version>1.8.1</version>
</dependency>

Anything else we need to know?