cpan: Do not parse intrinsic metadata for getting module author

Parsing perl module metadata files trigger a lot of errors due to badly formatted JSON or YAML and module author info is already provided by the cpan lister as extra loader arguments so remove that no longer needed metadata parsing step.

Related to swh-lister#2833

Depends on !338 (closed)

---

Migrated from D8651 (view on Phabricator)