Cursor: clean up cursor theme loading

wlroots will now load xcursor themes at the correct scale automatically
based on the scale of the outputs where ther cursors are displayed.

Also make the error handling a bit more robust.

river/Output.zig

@@ -306,15 +306,6 @@ pub fn create(wlr_output: *wlr.Output) !void {
     wlr_output.events.frame.add(&output.frame);
     wlr_output.events.present.add(&output.present);
 
-    // Ensure that a cursor image at the output's scale factor is loaded
-    // for each seat.
-    var it = server.input_manager.seats.first;
-    while (it) |seat_node| : (it = seat_node.next) {
-        const seat = &seat_node.data;
-        seat.cursor.xcursor_manager.load(wlr_output.scale) catch
-            log.err("failed to load xcursor theme at scale {}", .{wlr_output.scale});
-    }
-
     output.setTitle();
 
     output.active_link.init();