Game Display: removed unused variable

No idea what this did. It was added 11 years ago (9f11735f32)
but became unused at some point.

src/game_display.cpp

@@ -64,7 +64,6 @@ game_display::game_display(game_board& board, std::weak_ptr<wb::manager> wb,
 	, hex_def_fl_labels_()
 	, route_()
 	, displayedUnitHex_()
-	, sidebarScaling_(1.0)
 	, first_turn_(true)
 	, in_game_(false)
 	, chat_man_(new display_chat_manager(*this))

src/game_display.hpp

@@ -218,8 +218,6 @@ private:
 
 	map_location displayedUnitHex_;
 
-	double sidebarScaling_;
-
 	bool first_turn_, in_game_;
 
 	const std::unique_ptr<display_chat_manager> chat_man_;