Remove machine/stdarg.h includes that crept in after e453e498cbb8 due to
a lack of deprecation warnings (coming soon to a tree near you now that
sys/stdarg.h is in all releases we build packages for).
Sponsored by: DARPA, AFRL
Fixes: 15925062e1ba ("biosboot: Detect memory disks from PXE")
Fixes: 2ed9833791f2 ("thunderbolt: Import USB4 code")