Remove hardcoded kernel/filesystem

x86_64/livedisk.asm

-%include "bootsector.asm"
-
-startup_start:
-%ifdef ARCH_i386
-    %include "startup-i386.asm"
-%endif
-
-%ifdef ARCH_x86_64
-    %include "startup-x86_64.asm"
-%endif
-align 512, db 0
-startup_end:
-
-kernel_file:
-  incbin "build/kernel_live"
-  align 512, db 0
-.end:
-.length equ kernel_file.end - kernel_file
-.length_sectors equ .length / 512