build: don't compile with -Wno-uninitialized on darwin

This flag has been enabled for Darwin targets since the initial commit
in 4ed70a930202b103e7e80b8dc925e0aaa4622595. However, aside from the
fact that we likely no longer want to suppress uninitialized warnings,
this flag wont suppress them anyways, as it's included in the
CXX flags before -Wall (which enables -Wuninitialized). i.e:

```bash
g++ -std=gnu++11 ... -Wno-uninitialized ... -Wall <rest of flags>
```

configure.ac

@@ -280,9 +280,6 @@ case "${host_os}" in
         libzmq_pedantic="no"
         libzmq_werror="no"
         AC_DEFINE(ZMQ_HAVE_OSX, 1, [Have DarwinOSX OS])
-        AC_LANG_PUSH([C++])
-        LIBZMQ_CHECK_LANG_FLAG_PREPEND([-Wno-uninitialized])
-        AC_LANG_POP([C++])
         ;;
     *haiku*)
         AC_DEFINE(ZMQ_HAVE_HAIKU, 1, [Have Haiku OS])