Delete README.md

Remove out-of-date readme file.

apm-sniffer/apm-sdk-plugin/README.md

-|插件名称|功能|配置说明|版本与下载|
-| ----------- |---------| ----------|----------|
-|web-plugin|追踪指定的url访问| [查看](web-plugin) |[ ![Download](https://api.bintray.com/packages/wu-sheng/skywalking/com.ai.cloud.skywalking-web-plugin/images/download.svg) ](https://bintray.com/wu-sheng/skywalking/com.ai.cloud.skywalking-web-plugin/_latestVersion) |
-|spring-plugin| 追踪spring托管的类实例 | [查看](spring-plugin) |[ ![Download](https://api.bintray.com/packages/wu-sheng/skywalking/com.ai.cloud.skywalking-spring-plugin/images/download.svg) ](https://bintray.com/wu-sheng/skywalking/com.ai.cloud.skywalking-spring-plugin/_latestVersion) |
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-- 绝大多数插件，已经集成到skywalking-agent中，无需单独引入即可生效。
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