column-chooser: Port to G_DECLARE* type declaration

Currently, the type declaration is done manually. This patch reduces the no. of macros being used and improves
readability. It removes NautilusColumnChooserClass struct and changes the NautilusColumnChooser's type to
final as there is no need for data-hiding here, and it is not being subclassed anywhere.

https://bugzilla.gnome.org/show_bug.cgi?id=777609