Move download command to extension host

src/vs/workbench/api/browser/extensionHost.contribution.ts

@@ -48,6 +48,7 @@ import './mainThreadStorage';
 import './mainThreadTelemetry';
 import './mainThreadTerminalService';
 import './mainThreadTreeViews';
+import './mainThreadDownloadService';
 import './mainThreadUrls';
 import './mainThreadWindow';
 import './mainThreadWebview';