bind/objc: fix compile warning

An extra struct initializer was left over from an earlier version
of the direct call conversion. Remove it.

Change-Id: I19c3eb3be7bf78378af47ea182931b0c24cdd34d
Reviewed-on: https://go-review.googlesource.com/21104
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/objc/seq_darwin.m.support

@@ -157,7 +157,7 @@ int32_t go_seq_go_to_refnum(GoSeqRef *ref) {
 }
 
 nbyteslice go_seq_from_objc_bytearray(NSData *data, int copy) {
-  struct nbyteslice res = {NULL, 0, NO};
+  struct nbyteslice res = {NULL, 0};
   int sz = data.length;
   if (sz == 0) {
     return res;