WebXRManager: Remove old THREE call and add Matrix import statement

src/renderers/webvr/WebXRManager.js

@@ -8,6 +8,7 @@ import { ArrayCamera } from '../../cameras/ArrayCamera.js';
 import { PerspectiveCamera } from '../../cameras/PerspectiveCamera.js';
 import { WebGLAnimation } from '../webgl/WebGLAnimation.js';
 import { setProjectionFromUnion } from './WebVRUtils.js';
+import { Matrix4 } from '../../math/Matrix4';
 
 function WebXRManager( renderer ) {
 
@@ -303,7 +304,7 @@ function WebXRManager( renderer ) {
 	this.getStandingMatrix = function () {
 
 		console.warn( 'THREE.WebXRManager: getStandingMatrix() is no longer needed.' );
-		return new THREE.Matrix4();
+		return new Matrix4();
 
 	};