virutil.c: do not include stdarg.h

Last functions using it were moved to virfile.c in commit <bfe7721d>.
Signed-off-by: NJán Tomko <jtomko@redhat.com>

src/util/virutil.c

@@ -28,7 +28,6 @@
 
 #include <stdlib.h>
 #include <stdio.h>
-#include <stdarg.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>