Remove usage of no-op macro DEFINE_WEB_STATE_USER_DATA_KEY.

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

This CL was uploaded by git cl split.

R=vabr@chromium.org

Bug: 589840
Change-Id: I4269a5dcd85ae4e00d275c30fd40b622cc03a1ba
Reviewed-on: https://chromium-review.googlesource.com/c/1351951Reviewed-by: Vaclav Brozek <vabr@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611198}

ios/chrome/browser/passwords/password_tab_helper.mm

@@ -12,8 +12,6 @@
 #error "This file requires ARC support."
 #endif
 
-DEFINE_WEB_STATE_USER_DATA_KEY(PasswordTabHelper);
-
 PasswordTabHelper::~PasswordTabHelper() = default;
 
 // static