Remove wlr_presentation in sway_server struct

It is no longer in use.

include/sway/server.h

@@ -82,8 +82,6 @@ struct sway_server {
 	struct wlr_drm_lease_v1_manager *drm_lease_manager;
 	struct wl_listener drm_lease_request;
 
-	struct wlr_presentation *presentation;
-
 	struct wlr_pointer_constraints_v1 *pointer_constraints;
 	struct wl_listener pointer_constraint;
 

sway/server.c

@@ -259,8 +259,7 @@ bool server_init(struct sway_server *server) {
 	wl_signal_add(&server->pointer_constraints->events.new_constraint,
 		&server->pointer_constraint);
 
-	server->presentation =
-		wlr_presentation_create(server->wl_display, server->backend);
+	wlr_presentation_create(server->wl_display, server->backend);
 
 	server->output_manager_v1 =
 		wlr_output_manager_v1_create(server->wl_display);