Remove nonstandard <err.h>.

This provides some really nice functions, but does not exist in some
environments (particularly MinGW).

src/asm/yaccprt1.y

@@ -1,6 +1,5 @@
 %{
 #include <ctype.h>
-#include <err.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>