Remove unnecessary if statements in TFA validation logic

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Summary of the changes: Remove unnecessary if statements in TFA validation

Description

This pull request simplifies the Two-Factor Authentication (TFA) validation logic in ASP.NET Core Identity by removing unnecessary if statements. The main change is:

1. Removed the redundant else if statements, replacing them with direct if checks.

This change offers the following benefits:

• Improved readability: The code is now more straightforward and easier to follow.
• Reduced nesting: Eliminating the else statements reduces the complexity of the code structure.
• Better performance: The code now avoids unnecessary condition checks.

The modification does not alter the existing functionality or error messages. It simply removes redundant conditional statements to make the code more efficient.