replace include guards with pragma once

src/frontend/ContentGfxCache.hpp

@@ -1,5 +1,4 @@
-#ifndef FRONTEND_BLOCKS_GFX_CACHE_HPP_
-#define FRONTEND_BLOCKS_GFX_CACHE_HPP_
+#pragma once
 
 #include "typedefs.hpp"
 
@@ -23,5 +22,3 @@ public:
     
     const Content* getContent() const;
 };
-
-#endif // FRONTEND_BLOCKS_GFX_CACHE_HPP_