[windows] Eliminate unnecessary iostream imports (#38824)

In cd1a1cb I replaced use of direct writes to cerr and replaced them
with FML_LOG calls but may have missed removing some iostream #includes,
or they may have been missed in previous cleanups. This removes any
remaining #includes of iostream that are unused.

Author: cbracken

shell/platform/windows/flutter_window.h

@@ -5,7 +5,6 @@
 #ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_FLUTTER_WINDOW_H_
 #define FLUTTER_SHELL_PLATFORM_WINDOWS_FLUTTER_WINDOW_H_
 
-#include <iostream>
 #include <string>
 #include <vector>
 

shell/platform/windows/flutter_windows.cc

@@ -10,7 +10,6 @@
 #include <chrono>
 #include <cstdlib>
 #include <filesystem>
-#include <iostream>
 #include <memory>
 #include <vector>
 

shell/platform/windows/flutter_windows_engine.cc

@@ -7,7 +7,6 @@
 #include <dwmapi.h>
 
 #include <filesystem>
-#include <iostream>
 #include <sstream>
 
 #include "flutter/fml/logging.h"

shell/platform/windows/flutter_windows_texture_registrar_unittests.cc

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include <iostream>
-
 #include "flutter/fml/synchronization/waitable_event.h"
 #include "flutter/shell/platform/embedder/test_utils/proc_table_replacement.h"
 #include "flutter/shell/platform/windows/flutter_windows_engine.h"

shell/platform/windows/flutter_windows_view_unittests.cc

@@ -10,7 +10,6 @@
 #include <oleacc.h>
 
 #include <future>
-#include <iostream>
 #include <vector>
 
 #include "flutter/shell/platform/common/json_message_codec.h"

shell/platform/windows/keyboard_key_embedder_handler.cc

@@ -7,7 +7,6 @@
 #include <windows.h>
 
 #include <chrono>
-#include <iostream>
 #include <string>
 
 #include "flutter/fml/logging.h"