chore: remove Windows 8.1, Windows 10 LTSC and Windows Server 2012 R2

[flexiondotorg]

Description

The patch removes support for the following versions of Windows:

• Windows 8.1, which has been EOL since January 10, 2023.
• Windows 10 LTSC, which is intended for large-scale, long-term enterprise deployments and makes little to no sense for a virtual machine.
  • The Windows 10 LTSC support in Quickemu also lacked VirtIO and automated installation.
  • Regular Windows 10 is still available in Quickemu.
• Windows Server 2012 R2 which is EOL since October 10, 2023.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (updates documentation)

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation