ABMHandler and player_collisions use sequential read/write. Switch from std::list to std::vector

* Also remove dead code Map::unloadUnusedData which is dead since a long time

src/environment.h

@@ -393,7 +393,7 @@ private:
 	u32 m_game_time;
 	// A helper variable for incrementing the latter
 	float m_game_time_fraction_counter;
-	std::list<ABMWithState> m_abms;
+	std::vector<ABMWithState> m_abms;
 	// An interval for generally sending object positions and stuff
 	float m_recommended_send_interval;
 	// Estimate for general maximum lag as determined by server.