cleanup - remove send_tun()

Test:
  git grep send_tun
  comes up empty

Bug: 144730808
Test: atest clatd_test netd_integration_test
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: If81ca18bf5a33549b532de0d6406e32f4560c93a
diff --git a/translate.c b/translate.c
index 1632753..f759726 100644
--- a/translate.c
+++ b/translate.c
@@ -524,7 +524,7 @@
     if (iov_len > 0) {
       fill_tun_header(&tun_targ, ETH_P_IP);
       out[CLAT_POS_TUNHDR].iov_len = sizeof(tun_targ);
-      send_tun(fd, out, iov_len);
+      writev(fd, out, iov_len);
     }
   }
 }