Don't treat backgrounds as shell surfaces

This code had some issues. Remove it now so that we can start clean and fix
it later.

include/extensions.h

@@ -11,8 +11,6 @@ struct background_config {
 	wlc_resource surface;
 	// we need the wl_resource of the surface in the destructor
 	struct wl_resource *wl_surface_res;
-	// used to determine if client is a background
-	struct wl_client *client;
 };
 
 struct panel_config {

sway/extensions.c

@@ -73,7 +73,6 @@ static void set_background(struct wl_client *client, struct wl_resource *resourc
 	}
 	sway_log(L_DEBUG, "Setting surface %p as background for output %d", surface, (int)output);
 	struct background_config *config = malloc(sizeof(struct background_config));
-	config->client = client;
 	config->output = output;
 	config->surface = wlc_resource_from_wl_surface_resource(surface);
 	config->wl_surface_res = surface;

sway/handlers.c

@@ -176,17 +176,6 @@ static void handle_output_focused(wlc_handle output, bool focus) {
 	}
 }
 
-static bool client_is_background(struct wl_client *client) {
-	int i;
-	for (i = 0; i < desktop_shell.backgrounds->length; i++) {
-		struct background_config *config = desktop_shell.backgrounds->items[i];
-		if (config->client == client) {
-			return true;
-		}
-	}
-	return false;
-}
-
 static bool client_is_panel(struct wl_client *client) {
 	int i;
 	for (i = 0; i < desktop_shell.panels->length; i++) {
@@ -229,7 +218,7 @@ static bool handle_view_created(wlc_handle handle) {
 	struct wl_client *client = wlc_view_get_wl_client(handle);
 	pid_t pid;
 
-	if (client_is_background(client) || client_is_panel(client)) {
+	if (client_is_panel(client)) {
 		return true;
 	}