Remove dead Windows 7 conditions and inline CheckKeyConsistency in PfxFormatTests

[Copilot]

Description

Two places in PfxFormatTests.cs had an always-false condition OperatingSystem.IsWindows() && !PlatformDetection.IsWindows guarding followup = null. Since these can never be true, the followup variable was always CheckKeyConsistency and never modified.

• Removed both dead if blocks and their associated Windows 7 comment blocks
• Eliminated the intermediate Action<X509Certificate2> followup variable
• Passed CheckKeyConsistency directly to ReadMultiPfx calls

Before:

Action<X509Certificate2> followup = CheckKeyConsistency;

// For unknown reasons, CheckKeyConsistency on this test fails
// on Windows 7 with an Access Denied in all variations for
// Collections, and in invertCertOrder: true for Single.
//
// Obviously this hit some sort of weird corner case in the Win7
// loader, but it's not important to the test.

if (OperatingSystem.IsWindows() &&
    !PlatformDetection.IsWindows)
{
    followup = null;
}

ReadMultiPfx(pfxBytes, pw, first, expectedOrder, followup);

After:

ReadMultiPfx(pfxBytes, pw, first, expectedOrder, CheckKeyConsistency);

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[vcsjones]

This was just incomplete cleanup done in #122907.

[Copilot]

Pull request overview

Cleans up dead/unreachable Windows 7-specific code paths in PfxFormatTests by removing an always-false condition and simplifying the callback wiring used by ReadMultiPfx.

Changes:

• Removed the dead OperatingSystem.IsWindows() && !PlatformDetection.IsWindows branches (and associated Windows 7 comments).
• Eliminated the intermediate followup delegate variable.
• Passed CheckKeyConsistency directly into ReadMultiPfx calls.