16.0 Advanced Search: Remove deprecated fields from Elasticsearch

Background

There are a few deprecated fields that are not used in Advanced Search indexing or searching:

• namespace_ancestry in issue_config.rb (namespace_ancestry_ids this is confirmed in issue_instance_proxy.rb
• namespace_ancestry_ids in config.rb (traversal_ids is the field used, this is confirmed in the gitlab-elasticsearch-indexer

Proposal

• Remove the fields from the config files

Notes:

• Performing a zero-downtime reindexing in production to remove the fields from the index will not be a part of this work. That will be handled in a separate issue
• This change will only affect newly created indexes, existing indexes will continue to have the fields present. they can be removed by creating the index from scratch or performing a zero-downtime reindex. There is no harm in leaving the fields in an existing index.