[iOS Enterprise] Remove useless import and deps

A small fix cleaning up the password related imports and deps since we automate policy unittests and no longer need them for policy_unittest.mm.

Change-Id: Ic6a57e571a121c486b1edddc7b6d73c8713ff469
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2152906Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: sebsg <sebsg@chromium.org>
Commit-Queue: Tina Wang <tinazwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759781}

ios/chrome/browser/policy/BUILD.gn

@@ -91,7 +91,6 @@ source_set("unit_tests") {
     ":test_support",
     "//base",
     "//base/test:test_support",
-    "//components/password_manager/core/common",
     "//components/policy/core/browser:test_support",
     "//components/pref_registry",
     "//components/prefs",

ios/chrome/browser/policy/policy_unittest.mm

@@ -12,7 +12,6 @@
 #include "base/run_loop.h"
 #include "base/test/task_environment.h"
 #include "base/threading/thread_task_runner_handle.h"
-#include "components/password_manager/core/common/password_manager_pref_names.h"
 #include "components/policy/core/browser/policy_pref_mapping_test.h"
 #include "components/policy/core/common/mock_configuration_policy_provider.h"
 #include "components/policy/core/common/policy_map.h"