Clean up legacy v4.* and v5.* tags

[alexskr]

The current version of ontologies_api_ruby_client is v2.x (latest v2.7.0). There are legacy tags (v4., v5.) left over from when the ontologies_api_ruby_client and bioportal_web_ui versions were synchronized. We no longer maintain that linkage, and the old tags are confusing.

I propose to delete v4* and v5* tags