Change house GUI picker logic to be more like object GUI window.

Deselect house on object placement abort.
Set object placement on init or house selection.
Adjust display to still work even if no house selected,
by continuing to show the previous selection.

src/town_gui.h

@@ -12,11 +12,6 @@
 #ifndef TOWN_GUI_H
 #define TOWN_GUI_H
 
-#include "tile_type.h"
-
-struct Window;
-
-void ShowBuildHousePicker(Window *parent);
-void PlaceProc_House(TileIndex tile);
+void ShowBuildHousePicker();
 
 #endif /* TOWN_GUI_H */