Remove encoding='ascii' (#4413)

* Remove `encoding='ascii'`

* Reinstate `encoding='ascii'` in emojis()

utils/datasets.py

@@ -931,7 +931,7 @@ def dataset_stats(path='coco128.yaml', autodownload=False, verbose=False, profil
         im.save(im_dir / Path(f).name, quality=75)  # save
 
     zipped, data_dir, yaml_path = unzip(Path(path))
-    with open(check_file(yaml_path), encoding='ascii', errors='ignore') as f:
+    with open(check_file(yaml_path), errors='ignore') as f:
         data = yaml.safe_load(f)  # data dict
         if zipped:
             data['path'] = data_dir  # TODO: should this be dir.resolve()?