Remove remaining usage of cursor_to_dict. (#16564)

changelog.d/16564.misc

synapse/handlers/admin.py

synapse/handlers/room_list.py

synapse/handlers/room_summary.py

synapse/rest/admin/media.py

synapse/rest/admin/registration_tokens.py

synapse/rest/admin/rooms.py

synapse/rest/admin/users.py

synapse/storage/background_updates.py

synapse/storage/database.py

synapse/storage/databases/main/__init__.py

synapse/storage/databases/main/devices.py

synapse/storage/databases/main/media_repository.py

synapse/storage/databases/main/registration.py

synapse/storage/databases/main/room.py

tests/handlers/test_register.py

tests/storage/test_main.py

tests/storage/test_room.py