Remove deprecated MetaData/variable_names variable #92
Description
The obs2ioda library currently includes the variable MetaData/variable_names in its output files. This variable is deprecated and no longer allowed under the IODA v3 schema.
Including it results in the following schema validation error:
ERROR: Variable 'MetaData/variable_names' is deprecated and should be removed.
Context
This variable was previously used to enumerate field names but has since been replaced by schema-aware group and variable definitions in IODA v3.
Priority
Medium — not currently causing runtime failures, but blocks full schema compliance and generates validation errors.