search: Junk the OpenSearch system

The original design for the overview had buttons for searching for
Wikipedia and Google, but in practice this is a bad idea. The buttons
are the default activations, meaning that using the overview as a
fluent motion of launching something - "firefxo<Enter>", will launch
Google/Wikipedia.

https://bugzilla.gnome.org/show_bug.cgi?id=670168

src/shell-util.h

@@ -33,13 +33,6 @@ gboolean shell_write_string_to_stream          (GOutputStream    *stream,
 char    *shell_get_file_contents_utf8_sync     (const char       *path,
                                                 GError          **error);
 
-gboolean shell_parse_search_provider           (const char       *data,
-                                                char            **name,
-                                                char            **url,
-                                                GList           **langs,
-                                                char            **icon_data_uri,
-                                                GError          **error);
-
 gboolean shell_session_is_active_for_systemd (void);
 
 gboolean shell_util_wifexited                  (int               status,