Re-enable the browsertest UsbStickUpdateAppNoNetwork

We did some refactoring for Chrome app Kiosk. UsbStickUpdateAppNoNetwork
case can pass stably in local now. Please let me re-enable it and keep
monitoring.

Bug: 1021492
Change-Id: Icfeaf4ca83de0f0b71208588b25775a73802ab50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2396126Reviewed-by: Anatoliy Potapchuk <apotapchuk@chromium.org>
Commit-Queue: Anqing Zhao <anqing@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804889}

chrome/browser/chromeos/login/app_mode/kiosk_browsertest.cc

@@ -2085,7 +2085,7 @@ IN_PROC_BROWSER_TEST_F(KioskUpdateTest, PRE_UsbStickUpdateAppNoNetwork) {
 }
 
 // Restart the device, verify the app has been updated to v2.
-IN_PROC_BROWSER_TEST_F(KioskUpdateTest, DISABLED_UsbStickUpdateAppNoNetwork) {
+IN_PROC_BROWSER_TEST_F(KioskUpdateTest, UsbStickUpdateAppNoNetwork) {
   // Verify the kiosk app has been updated to v2.
   set_test_app_id(kTestOfflineEnabledKioskApp);
   StartUIForAppLaunch();