remove unused member (dead code)

src/play_controller.cpp

@@ -116,7 +116,6 @@ play_controller::play_controller(const config& level, saved_game& state_of_game,
 	statistics_context_(level["name"]),
 	undo_stack_(new actions::undo_list(level.child("undo_stack"))),
 	whiteboard_manager_(),
-	xp_mod_(level["experience_modifier"].to_int(100)),
 	loading_game_(level["playing_team"].empty() == false),
 	first_human_team_(-1),
 	player_number_(1),

src/play_controller.hpp

@@ -248,7 +248,6 @@ protected:
 	//whiteboard manager
 	boost::shared_ptr<wb::manager> whiteboard_manager_;
 
-	const unit_type::experience_accelerator xp_mod_;
 	//if a team is specified whose turn it is, it means we're loading a game
 	//instead of starting a fresh one. Gets reset to false after init_side
 	bool loading_game_;