fix(material/testing): Remove unused reference to documentRootLocatorFactory

Author: wildcardalice

src/material/input/testing/input-harness.ts

@@ -13,8 +13,6 @@ import {InputHarnessFilters} from './input-harness-filters';
 
 /** Harness for interacting with a standard Material inputs in tests. */
 export class MatInputHarness extends MatFormFieldControlHarnessBase {
-  private readonly _documentRootLocator = this.documentRootLocatorFactory();
-
   // TODO: We do not want to handle `select` elements with `matNativeControl` because
   // not all methods of this harness work reasonably for native select elements.
   // For more details. See: https://github.com/angular/components/pull/18221.