Remove usage of no-op macro DEFINE_WEB_STATE_USER_DATA_KEY.

This CL removes macro usage from /ios/chrome/browser/history.

This CL was uploaded by git cl split.

R=sczs@chromium.org

Bug: 589840
Change-Id: I8f5c3e1980e622a55202a76db722dd65bcf348e4
Reviewed-on: https://chromium-review.googlesource.com/c/1351960Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611288}

ios/chrome/browser/history/history_tab_helper.mm

@@ -24,8 +24,6 @@
 #error "This file requires ARC support."
 #endif
 
-DEFINE_WEB_STATE_USER_DATA_KEY(HistoryTabHelper);
-
 namespace {
 
 base::Optional<base::string16> GetPageTitle(const web::NavigationItem& item) {