Remove Qt Windows Extra for Qt 6 and later

[tommyvct]

Description

Remove Qt Windows Extra for Qt 6 and later

Motivation and Context

Qt 6 and later removed platform-specific extra modules from the code base.

How Has This Been Tested?

It compiles.
Tested on Windows 10 x64 and 11 ARM64 without crash.

Types of changes

• Tweak (non-breaking change to improve existing functionality)

• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[WizardCM]

I can't decide if it's fine to have the same check written multiple times, or if there should be a variable that's reused instead.