Move date_h to pragma once

Change-Id: I04864e8c47c8bb1763016b6ba1e5826450afdc72
Signed-off-by: Ed Tanous <edtanous@google.com>
diff --git a/redfish-core/include/utils/extern/date.h b/redfish-core/include/utils/extern/date.h
index ebeaeb1..23f7d0c 100644
--- a/redfish-core/include/utils/extern/date.h
+++ b/redfish-core/include/utils/extern/date.h
@@ -1,3 +1,4 @@
+#pragma once
 // NOLINTBEGIN
 // clang-format off
 
@@ -6,9 +7,6 @@
  *  https://github.com/HowardHinnant/date/blob/master/include/date/date.h
  */
 
-#ifndef DATE_H
-#define DATE_H
-
 // The MIT License (MIT)
 //
 // Copyright (c) 2015, 2016, 2017 Howard Hinnant
@@ -8250,5 +8248,3 @@
 
 // NOLINTEND
 // clang-format off
-
-#endif  // DATE_H