refactor: Remove unused libmedia proxy and related files

docs/assets/example/libmedia.js

@@ -1,11 +0,0 @@
-// From: https://github.com/zhaohappy/libmedia
-// npm i artplayer-proxy-libmedia
-// import artplayerProxyLibmedia from 'artplayer-proxy-libmedia';
-
-var art = new Artplayer({
-    container: '.artplayer-app',
-    url: '/assets/sample/video.mp4',
-    proxy: artplayerProxyLibmedia({
-        //
-    }),
-});