Remove SigninManager's leftover includes from EPK private API

There is no piece of code currently using the SigninManager so we can
safely remove them.

Bug: 920207
Change-Id: If1235d83211c15c02f0fbafc5ec9b6a02125565e
Reviewed-on: https://chromium-review.googlesource.com/c/1407700
Reviewed-by: Mattias Nissler <mnissler@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#624800}
diff --git a/chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.cc b/chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.cc
index 69aecb41..a080708 100644
--- a/chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.cc
+++ b/chrome/browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.cc
@@ -19,7 +19,6 @@
 #include "chrome/browser/chromeos/settings/cros_settings.h"
 #include "chrome/browser/extensions/chrome_extension_function_details.h"
 #include "chrome/browser/profiles/profile.h"
-#include "chrome/browser/signin/signin_manager_factory.h"
 #include "chrome/common/extensions/api/enterprise_platform_keys_private.h"
 #include "chrome/common/pref_names.h"
 #include "chromeos/attestation/attestation_flow.h"
@@ -34,7 +33,6 @@
 #include "components/account_id/account_id.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/prefs/pref_service.h"
-#include "components/signin/core/browser/signin_manager.h"
 #include "components/user_manager/known_user.h"
 #include "components/user_manager/user.h"
 #include "components/user_manager/user_manager.h"