RFR: 8289770: Remove Windows version macro from ShellFolder2.cpp

[Sergey Bylokhov]

On Thu, 11 Apr 2024 09:33:09 GMT, Alexey Ivanov <aivanov at openjdk.org> wrote:

> This clean-up PR removes unused Windows version macro from `ShellFolder2.cpp`.
> 
> `IS_WINVISTA` was not used at all.
> 
> `IS_WINXP` guarded support for icons with alpha channel. It is now safe to assume Java runs on a Windows version later than Windows XP. Java launchers specify 6.0 as the minimum OS version which corresponds to Windows Vista.

Marked as reviewed by serb (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/18736#pullrequestreview-2008154224