CommonSettings.php sets $wgLicenseURL, however this variable is not used anywhere. Instead, Collection uses $wgCollectionLicenseURL which defaults to null and therefore MediaWiki's config ($wgRights*) is getting used for attribution in PDFs. From this, it seems like $wgLicense should just be dropped.
Customize query in gerrit
|operations/mediawiki-config||master||+0 -2||Cleanup: Stop trying to set wgLicenseURL, never read|