refactor(@angular/cli): remove unused package-tree utilities

This commit removes the unused `package-tree.ts` utilities, including `getProjectDependencies`, `readPackageJson`, and `PackageTreeNode`.
The `findPackageJson` function, which was the only remaining used part, has been moved directly into `commands/update/cli.ts` where it is consumed.

Author: clydin

packages/angular/cli/src/commands/update/cli.ts

@@ -29,7 +29,6 @@ import {
 import { colors } from '../../utilities/color';
 import { disableVersionCheck } from '../../utilities/environment-options';
 import { assertIsError } from '../../utilities/error';
-import { findPackageJson } from '../../utilities/package-tree';
 import {
   checkCLIVersion,
   coerceVersionNumber,
@@ -697,3 +696,14 @@ async function readPackageManifest(manifestPath: string): Promise<PackageManifes
     return undefined;
   }
 }
+
+function findPackageJson(workspaceDir: string, packageName: string): string | undefined {
+  try {
+    const projectRequire = createRequire(path.join(workspaceDir, 'package.json'));
+    const packageJsonPath = projectRequire.resolve(`${packageName}/package.json`);
+
+    return packageJsonPath;
+  } catch {
+    return undefined;
+  }
+}