WebVR.js: Removed unused variable.

examples/js/vr/WebVR.js

@@ -128,12 +128,8 @@ var WEBVR = {
 
 		}
 
-		var isWebXR = false;
-
 		if ( 'xr' in navigator ) {
 
-			isWebXR = true;
-
 			var button = document.createElement( 'button' );
 			button.style.display = 'none';