[ie] Migrate commonly plural fields to lists (#8917)

Authored by: llistochek, pukkandan
Related: #3944

test/helper.py

@@ -223,6 +223,10 @@ def sanitize_got_info_dict(got_dict):
     if test_info_dict.get('display_id') == test_info_dict.get('id'):
         test_info_dict.pop('display_id')
 
+    # Remove deprecated fields
+    for old in YoutubeDL._deprecated_multivalue_fields.keys():
+        test_info_dict.pop(old, None)
+
     # release_year may be generated from release_date
     if try_call(lambda: test_info_dict['release_year'] == int(test_info_dict['release_date'][:4])):
         test_info_dict.pop('release_year')

test/test_YoutubeDL.py

@@ -941,7 +941,7 @@ class TestYoutubeDL(unittest.TestCase):
         def get_videos(filter_=None):
             ydl = YDL({'match_filter': filter_, 'simulate': True})
             for v in videos:
-                ydl.process_ie_result(v, download=True)
+                ydl.process_ie_result(v.copy(), download=True)
             return [v['id'] for v in ydl.downloaded_info_dicts]
 
         res = get_videos()