Replace simple serial-based menu with system detection logic using whichsys.c32 to automatically select between PXE and direct system boot. This enables dynamic boot method selection while maintaining support for both boot scenarios.
BREAKING CHANGE: Changes syslinux.cfg structure from single menu-based boot to conditional boot selection. Systems relying on the previous serial menu interface and default 'arch' label will need to adapt to the new whichsys-based selection mechanism.
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