draft: updates: Spot updates for policykit by dropping its epoch

In the distant past Apertis shipped a policykit version from experimental that never landed to any Debian release.

More recently we moved back to the policykit version shipped in Debian releases, but to supersede the version from experimental an epoch was introduced downstream.

The epoch causes all comparison with the Debian version to fail, and updates are not detected.

Special-case this situation by dropping the epoch when doing the check.