[iOS] Clean deps and public_deps.

ios/chrome/browser/providers/signin/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 source_set("signin") {
   sources = [
     "chromium_signin_resources_provider.h",
     "chromium_signin_resources_provider.mm",
   ]
   deps = [
     "//base",
     "//ios/chrome/browser/ui",
-    "//ios/public/provider/chrome/browser",
+    "//ios/public/provider/chrome/browser/signin",
   ]
   libs = [ "UIKit.framework" ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }