Revert "sd-netlink: prepare buffer for dropping unexpected message"

This reverts commit bf478dcffb.

I think we should avoid allocating memory needlessly just to free it
again, in particular if this can be triggered by some rogue peer.

src/libsystemd/sd-netlink/netlink-socket.c

@@ -181,12 +181,6 @@ static int socket_recv_message(int fd, void *buf, size_t buf_size, uint32_t *ret
                 log_debug("sd-netlink: ignoring message from PID %"PRIu32, sender.nl.nl_pid);
 
                 if (peek) {
-                        _cleanup_free_ uint8_t *b = new(uint8_t, n);
-                        if (!b)
-                                return -ENOMEM;
-
-                        iov = IOVEC_MAKE(b, n);
-
                         /* drop the message */
                         n = recvmsg_safe(fd, &msg, 0);
                         if (n < 0)