Kernel: Remove includes to LibC stdarg definitions

We don't actually need the va_list and other stdarg definitions in the
kernel, because we actually don't use the "pure" printf interface in any
kernel code at all, but we retain the snprintf declaration because the
libstdc++ library still need it to be declared and extern'ed.

Kernel/KBufferBuilder.h

@@ -9,7 +9,6 @@
 #include <AK/StringBuilder.h>
 #include <AK/StringView.h>
 #include <Kernel/KBuffer.h>
-#include <stdarg.h>
 
 namespace Kernel {