security: Improve reliability of TPM BackEnd RandomKeyId test case

refs #4092

Change-Id: I58c6f3efbbbf31a826a7c41ede2494f0fbe313f1
diff --git a/tests/unit-tests/security/tpm/back-end.t.cpp b/tests/unit-tests/security/tpm/back-end.t.cpp
index f118099..6880a0b 100644
--- a/tests/unit-tests/security/tpm/back-end.t.cpp
+++ b/tests/unit-tests/security/tpm/back-end.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2017 Regents of the University of California.
+ * Copyright (c) 2013-2018 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -251,7 +251,6 @@
   for (int i = 0; i < 100; i++) {
     auto key = tpm.createKey(identity, RsaKeyParams());
     Name keyName = key->getKeyName();
-    tpm.deleteKey(keyName);
     BOOST_CHECK(keyNames.insert(keyName).second);
   }
 }