Remove usage of no-op macro DEFINE_WEB_STATE_USER_DATA_KEY.

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

This CL was uploaded by git cl split.

R=sdefresne@chromium.org

Bug: 589840
Change-Id: I60b22d3a7b65e614f6109a5d2a79baabe986724f
Reviewed-on: https://chromium-review.googlesource.com/c/1351076Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611211}

ios/chrome/browser/download/download_manager_tab_helper.mm

@@ -14,8 +14,6 @@
 #error "This file requires ARC support."
 #endif
 
-DEFINE_WEB_STATE_USER_DATA_KEY(DownloadManagerTabHelper);
-
 DownloadManagerTabHelper::DownloadManagerTabHelper(
     web::WebState* web_state,
     id<DownloadManagerTabHelperDelegate> delegate)

ios/chrome/browser/download/pass_kit_tab_helper.mm

@@ -20,8 +20,6 @@
 #error "This file requires ARC support."
 #endif
 
-DEFINE_WEB_STATE_USER_DATA_KEY(PassKitTabHelper);
-
 const char kUmaDownloadPassKitResult[] = "Download.IOSDownloadPassKitResult";
 
 namespace {