Remove unused variable, and fix a compilation warning on Windows

Modules/posixmodule.c

@@ -4083,7 +4083,7 @@ Kill a process with a signal.");
 static PyObject *
 win32_kill(PyObject *self, PyObject *args)
 {
-    PyObject *result, handle_obj;
+    PyObject *result;
     DWORD pid, sig, err;
     HANDLE handle;