Remove usage of no-op macro DEFINE_WEB_STATE_USER_DATA_KEY.

This CL removes macro usage from /ios/web_view.

This CL was uploaded by git cl split.

R=rohitrao@chromium.org

Bug: 589840
Change-Id: I91645c283c518b67e1a7efe866d30ba566815273
Reviewed-on: https://chromium-review.googlesource.com/c/1351965Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612310}

ios/web_view/internal/translate/web_view_translate_client.mm

@@ -32,8 +32,6 @@
 #error "This file requires ARC support."
 #endif
 
-DEFINE_WEB_STATE_USER_DATA_KEY(ios_web_view::WebViewTranslateClient);
-
 namespace ios_web_view {
 
 WebViewTranslateClient::WebViewTranslateClient(web::WebState* web_state)