appDisplay: Use the desktop file index for app searching

Rather than scanning all apps for searching, use Ryan's new desktop
file index and the glib support APIs for app searching instead of our
own system.

https://bugzilla.gnome.org/show_bug.cgi?id=711631

src/shell-util.h

@@ -19,10 +19,6 @@ void     shell_util_get_transformed_allocation (ClutterActor     *actor,
 
 int      shell_util_get_week_start             (void);
 
-char    *shell_util_normalize_and_casefold     (const char       *str);
-
-char    *shell_util_normalize_casefold_and_unaccent (const char  *str);
-
 char    *shell_util_format_date                (const char       *format,
                                                 gint64            time_ms);