refactor: Remove unused libmedia proxy and related files

CHANGELOG_CN.md

@@ -8,7 +8,6 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 -   新增 `option.proxy` 选项，用于代理第三方的 `video` 和 `canvas`
 -   新增 `artplayer-proxy-webav` 代理，来自 [bilibili/WebAV](https://github.com/bilibili/WebAV)
--   新增 `artplayer-proxy-libmedia` 代理，来自 [zhaohappy/libmedia](https://github.com/zhaohappy/libmedia)
 -   新增 `option.thumbnails.scale`, 用于预览图缩放
 -   修复更改 `art.url` 不能触发 `autoPlayBack` 的 `bug`: [#797](https://github.com/zhw2590582/ArtPlayer/issues/797)