ACPI: Drop ACPI_USE_BUILTIN_STDARG ifdef from acgcc.h

The ACPI_USE_BUILTIN_STDARG symbol is never set in the kernel build,
so stop checking it in include/acpi/platform/acgcc.h and drop all of
the macros depending on it (which appear to duplicate the analogous
macros from linux/stdarg.h, but in fact are never used).

Link: https://lore.kernel.org/linux-acpi/CAHk-=whCammRsz8PEbrft3M6vGjF506gkxtyGw81uGOUUvD51g@mail.gmail.com/
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Linus Torvalds <torvalds@linuxfoundation.org>