Fix a memory leak

pointed by @nobu

ext/socket/raddrinfo.c

@@ -688,7 +688,7 @@ rb_getnameinfo(const struct sockaddr *sa, socklen_t salen,
                char *serv, size_t servlen, int flags)
 {
     int retry;
-    struct getnameinfo_arg *arg = allocate_getnameinfo_arg(sa, salen, hostlen, servlen, flags);
+    struct getnameinfo_arg *arg;
     int err;
 
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