test(language-service): Remove unused code in test project (#37122)

This commit removes the `bootstrap()` function in the test project since
its presence has no effect on the behavior of language service.

Also removes the explicit cast when instantiating `CounterDirectiveContext`,
and let type inference takes care of that.

PR Close #37122

packages/language-service/test/project/app/main.ts

@@ -27,7 +27,3 @@ import * as ParsingCases from './parsing-cases';
 })
 export class AppModule {
 }
-
-declare function bootstrap(v: any): void;
-
-bootstrap(AppComponent);