Remove unused variable

New clang detects this unused variable.

https://ci.chromium.org/p/chromium/builders/luci.chromium.try/ios-device/4574
../../ios/chrome/browser/browser_state/chrome_browser_state_io_data.mm:86:7: error: unused variable 'iter' [-Werror,-Wunused-variable]
      iter;
      ^
1 error generated.

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I019c3ecf8677e4b93f8289a722686bc186476bfe
Reviewed-on: https://chromium-review.googlesource.com/1143172
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576443}

ios/chrome/browser/browser_state/chrome_browser_state_io_data.mm

@@ -82,8 +82,6 @@ void NotifyContextGettersOfShutdownOnIO(
         ChromeBrowserStateIOData::IOSChromeURLRequestContextGetterVector>
         getters) {
   DCHECK_CURRENTLY_ON(web::WebThread::IO);
-  ChromeBrowserStateIOData::IOSChromeURLRequestContextGetterVector::iterator
-      iter;
   for (auto& chrome_context_getter : *getters)
     chrome_context_getter->NotifyContextShuttingDown();
 }