Remove version from ComputerLanguage

[simleo]

This had several problems:

• version is not a property of ComputerLanguage
• We were using defaults, but no info is better than likely wrong info (see also Remove software version defaults #130)
• Workflow RO-Crate language samples also don't have version, though there the CWL identifier is hardcoded to https://w3id.org/cwl/v1.2/.

I left the lang_version argument of add_workflow untouched, so it can be used to set the version for the CWL identifier.

UPDATE (2023-05-29): At the latest meeting, some expressed concerns about removing the ability to set the version entirely, so I changed the PR to only remove the arbitrary defaults instead. Note that the identifier for the CWL language is versioned only if a version is provided, as in the original PR.