Fix an unused variable in NSPR

nspr/pr/src/io/prfdcach.c

 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "primpl.h"
 
 #include <string.h>
 
 /*****************************************************************************/
@@ skipping 195 matching lines @@
         _pr_fd_cache.limit_high = _pr_fd_cache.limit_low;
 
     _pr_fd_cache.ml = PR_NewLock();
     PR_ASSERT(NULL != _pr_fd_cache.ml);
 
 }  /* _PR_InitFdCache */
 
 void _PR_CleanupFdCache(void)
 {
     PRFileDesc *fd, *next;
-    PRStackElem *pop;
 
     for (fd = _pr_fd_cache.head; fd != NULL; fd = next)
     {
         next = fd->higher;
         PR_DELETE(fd->secret);
         PR_DELETE(fd);
     }
     _pr_fd_cache.head = NULL;
     _pr_fd_cache.tail = NULL;
     _pr_fd_cache.count = 0;
     PR_DestroyLock(_pr_fd_cache.ml);
     _pr_fd_cache.ml = NULL;
 }  /* _PR_CleanupFdCache */
 
 /* prfdcach.c */