Remove some configure header-file checks that we weren't really using.

We had some AC_CHECK_HEADER tests that were really wastes of cycles,
because the code proceeded to #include those headers unconditionally
anyway, in all or a large majority of cases.  The lack of complaints
shows that those headers are available on every platform of interest,
so we might as well let configure run a bit faster by not probing
those headers at all.

I suspect that some of the tests I left alone are equally useless, but
since all the existing #includes of the remaining headers are properly
guarded, I didn't touch them.

src/backend/libpq/ifaddr.c

@@ -322,9 +322,7 @@ pg_foreach_ifaddr(PgIfAddrCallback callback, void *cb_data)
 }
 #else							/* !HAVE_GETIFADDRS && !WIN32 */
 
-#ifdef HAVE_SYS_IOCTL_H
 #include <sys/ioctl.h>
-#endif
 
 #ifdef HAVE_NET_IF_H
 #include <net/if.h>