Remove redundant, fix spine

Author: aversey

docs/concepts/mlops/mlops.md

@@ -76,6 +76,7 @@ nav:
               - user_guides/fs/feature_group/index.md
               - Create: user_guides/fs/feature_group/create.md
               - Create External: user_guides/fs/feature_group/create_external.md
+              - Create Spine: user_guides/fs/feature_group/create_spine.md
               - Deprecate: user_guides/fs/feature_group/deprecation.md
               - Data Types and Schema management: user_guides/fs/feature_group/data_types.md
               - Statistics: user_guides/fs/feature_group/statistics.md