refactor(language-service): remove non-null assertion on MockHost member (#32666)

`nodeModulesPath` is now initialized in the constructor, so there is no
need for a non-null assertion as suggested in #24571.

PR Close #32666

packages/language-service/test/test_utils.ts

@@ -66,8 +66,7 @@ missingCache.set('/node_modules/@angular/forms/src/directives/form_interface.met
 
 export class MockTypescriptHost implements ts.LanguageServiceHost {
   private angularPath: string|undefined;
-  // TODO(issue/24571): remove '!'.
-  private nodeModulesPath !: string;
+  private nodeModulesPath: string;
   private scriptVersion = new Map<string, number>();
   private overrides = new Map<string, string>();
   private projectVersion = 0;