Revert "Use IMM32 instead of TSF on Win7."

This reverts commit 9a00ff2b.

Reason for revert: <INSERT REASONING HERE>
Merge to M75 beta is failed, so I need to reland it in master and then
try to merge it again to M75.

Original change's description:
> Use IMM32 instead of TSF on Win7.
> 
> On Windows 7, there are many IMM32-based IMEs are relying on IMM32
> support. We should continue supporting those legacy IMEs on Win7. We
> should disable TSF on Win7 and use IMM32. All other Windows platforms
> are not affected.
> 
> Bug: 963558
> Change-Id: I8f77afbdb734c355f4393880e80fafd98e25ae88
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1613974
> Reviewed-by: Yohei Yukawa <yukawa@chromium.org>
> Commit-Queue: Siye Liu <siliu@microsoft.com>
> Cr-Commit-Position: refs/heads/master@{#660261}

TBR=yukawa@chromium.org,siliu@microsoft.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 963558
Change-Id: I4341bed006e86e756a21997c167c9526c6ce2901
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1618010Reviewed-by: Lan Wei <lanwei@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660980}

ui/base/ime/init/input_method_factory.cc

@@ -6,7 +6,6 @@
 
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
-#include "base/win/windows_version.h"
 #include "build/build_config.h"
 #include "ui/base/ime/mock_input_method.h"
 #include "ui/base/ui_base_features.h"
@@ -60,10 +59,8 @@ std::unique_ptr<InputMethod> CreateInputMethod(
 #if defined(OS_CHROMEOS)
   return std::make_unique<InputMethodChromeOS>(delegate);
 #elif defined(OS_WIN)
-  if (base::FeatureList::IsEnabled(features::kTSFImeSupport) &&
-      base::win::GetVersion() > base::win::Version::WIN7) {
+  if (base::FeatureList::IsEnabled(features::kTSFImeSupport))
     return std::make_unique<InputMethodWinTSF>(delegate, widget);
-  }
   return std::make_unique<InputMethodWinImm32>(delegate, widget);
 #elif defined(OS_MACOSX)
   return std::make_unique<InputMethodMac>(delegate);