view: simplify code for applying the StyleScheme to the view
view: simplify code for applying the StyleScheme to the view

The style_scheme_applied instance variable was useful to defer the
action when the widget is realized. But it is no longer useful, after
commit 8568dabf9f380971eb8ca31d908e489ed0ce47fa.

GNOME/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,uajain/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview