Revert "is_ipv6_available: Create a fake zmq context on windows"

This reverts commit 9adf20aa.

tests/testutil.hpp

@@ -339,10 +339,6 @@ is_ipv6_available(void)
     inet_pton (AF_INET6, "::1", &(test_addr.sin6_addr));
 
 #ifdef ZMQ_HAVE_WINDOWS
-    // initialize network stack
-    void *ctx = zmq_ctx_new();
-    assert(ctx);
-
     SOCKET fd = socket (AF_INET6, SOCK_STREAM, IPPROTO_IP);
     if (fd == INVALID_SOCKET)
         ipv6 = 0;
@@ -358,9 +354,6 @@ is_ipv6_available(void)
         }
         closesocket (fd);
     }
-
-    rc = zmq_ctx_term(ctx);
-    assert(rc == 0);
 #else
     int fd = socket (AF_INET6, SOCK_STREAM, IPPROTO_IP);
     if (fd == -1)