Use direct members instead of pointers for viewableChunks and buyback

We had avoided putting STL containers into Players back when we thought
Players was still POD and needed to remain POD, but it turned out that
neither were the case all along, so there's no need for the indirection.

src/Player.hpp

@@ -83,10 +83,10 @@ struct Player {
     uint64_t iFirstUseFlag[2];
 
     ChunkPos chunkPos;
-    std::set<Chunk*> *viewableChunks;
+    std::set<Chunk*> viewableChunks;
     time_t lastHeartbeat;
 
     int suspicionRating;
     time_t lastShot;
-    std::vector<sItemBase> *buyback;
+    std::vector<sItemBase> buyback;
 };