Remove usage of no-op macro DEFINE_WEB_STATE_USER_DATA_KEY.

This CL removes macro usage from /ios/web/public/test.

This CL was uploaded by git cl split.

R=eugenebut@chromium.org

Bug: 589840
Change-Id: I507c145fbe39d32120bec413834873ed2d92604e
Reviewed-on: https://chromium-review.googlesource.com/c/1351963Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611311}

ios/web/public/test/test_redirect_observer.mm

@@ -15,8 +15,6 @@
 
 namespace web {
 
-DEFINE_WEB_STATE_USER_DATA_KEY(TestRedirectObserver);
-
 #pragma mark - TestRedirectObserver
 
 TestRedirectObserver::TestRedirectObserver(WebState* web_state) {