refactor(cli): remove enableImmutableInstalls override from .yarnrc.yml

Let yarn Berry use its default behavior to see what errors occur in CI
with immutable installs enabled.

Author: fengmk2

packages/cli/src/migration/migrator.ts

@@ -1125,11 +1125,6 @@ function rewriteYarnrcYml(projectPath: string): void {
     if (!doc.has('nodeLinker')) {
       doc.set('nodeLinker', 'node-modules');
     }
-    // Disable immutable installs so yarn can create/update lockfiles
-    // (yarn Berry defaults to enableImmutableInstalls: true in CI)
-    if (!doc.has('enableImmutableInstalls')) {
-      doc.set('enableImmutableInstalls', false);
-    }
     // catalog
     rewriteCatalog(doc);
   });