Remove artplayer-plugin-liquid-glass plugin

- Deleted the plugin files including JavaScript, CSS, README, and type definitions.
- Removed references to the plugin from the documentation.
- Cleaned up the package structure by removing the .npmignore and package.json files related to the plugin.

docs/assets/example/liquid.glass.js

@@ -1,30 +0,0 @@
-// npm i artplayer-plugin-liquid-glass
-// import artplayerPluginLiquidGlass from 'artplayer-plugin-liquid-glass';
-
-let art = new Artplayer({
-  container: '.artplayer-app',
-  url: '/assets/sample/video.mp4',
-  poster: '/assets/sample/poster.jpg',
-  autoSize: true,
-  pip: true,
-  setting: true,
-  fullscreen: true,
-  fullscreenWeb: true,
-  miniProgressBar: true,
-  flip: true,
-  playbackRate: true,
-  aspectRatio: true,
-  thumbnails: {
-    url: '/assets/sample/thumbnails.png',
-    number: 60,
-    column: 10,
-    scale: 0.8,
-  },
-  plugins: [
-    artplayerPluginLiquidGlass({
-      width: '75%',
-      'max-width': '640px',
-      'min-width': '320px',
-    }),
-  ],
-})