fix(cdk/tree): fix lint errors

Author: BobobUnicorn

src/cdk/tree/tree-redesign.spec.ts

@@ -5,7 +5,7 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-import {ComponentFixture, TestBed, fakeAsync, flush} from '@angular/core/testing';
+import {ComponentFixture, TestBed} from '@angular/core/testing';
 import {
   Component,
   ErrorHandler,

src/cdk/tree/tree.spec.ts

@@ -5,7 +5,7 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-import {ComponentFixture, TestBed, fakeAsync, flush} from '@angular/core/testing';
+import {ComponentFixture, TestBed} from '@angular/core/testing';
 import {
   Component,
   ErrorHandler,

src/cdk/tree/tree.ts

@@ -693,12 +693,12 @@ export class CdkTree<T, K = T> implements AfterContentChecked, CollectionViewer,
       // This flattens children into a single array.
       return observableOf(...nodes).pipe(
         concatMap(node => concat(observableOf([node]), this._getAllChildrenRecursively(node))),
-        reduce((results, nodes) => {
-          results.push(...nodes);
+        reduce((results, children) => {
+          results.push(...children);
           return results;
         }, [] as T[]),
-        tap(nodes => {
-          this._dataNodes.next(nodes);
+        tap(allNodes => {
+          this._dataNodes.next(allNodes);
         }),
       );
     } else if (this.levelAccessor && this.nodeType === 'nested') {