Delete unused files

docs/assets/ts/artplayer-plugin-vtt-thumbnail.d.ts

@@ -0,0 +1,10 @@
+import type Artplayer from 'artplayer';
+
+export = artplayerPluginVttThumbnail;
+export as namespace artplayerPluginVttThumbnail;
+
+declare const artplayerPluginVttThumbnail: (option: { vtt?: string; style?: Partial<CSSStyleDeclaration> }) => (
+    art: Artplayer,
+) => {
+    name: 'artplayerPluginVttThumbnail';
+};