Various code cleanup & little performance improvement on HTTP download (#5772)

* Disable or remove unused enum members/functions
* Tiny code style fixes
* Make some functions const
* Replace ClientMediaDownloader std::unordered_map with std::map

src/content_cao.h

@@ -146,19 +146,8 @@ public:
 
 	scene::ISceneNode *getSceneNode();
 
-	scene::IMeshSceneNode *getMeshSceneNode();
-
 	scene::IAnimatedMeshSceneNode *getAnimatedMeshSceneNode();
 
-	WieldMeshSceneNode *getWieldMeshSceneNode();
-
-	scene::IBillboardSceneNode *getSpriteSceneNode();
-
-	inline bool isPlayer() const
-	{
-		return m_is_player;
-	}
-
 	inline bool isLocalPlayer() const
 	{
 		return m_is_local_player;