Replace all include guard ifdefs with "#pragma once"

Source/Core/InputCommon/ControllerInterface/ExpressionParser.h

@@ -1,6 +1,8 @@
+// Copyright 2013 Dolphin Emulator Project
+// Licensed under GPLv2
+// Refer to the license.txt file included.
 
-#ifndef _EXPRESSIONPARSER_H_
-#define _EXPRESSIONPARSER_H_
+#pragma once
 
 #include <string>
 #include "Device.h"
@@ -65,5 +67,3 @@ ExpressionParseStatus ParseExpression(std::string expr, ControlFinder &finder, E
 
 }
 }
-
-#endif