Fix EZP-21509: error in clear view cache for subtree.

JIRA: https://jira.ez.no/browse/EZP-21509

Since EZP-18195 (https://github.com/ezsystems/ezpublish-legacy/commit/4652d45ca637239b4aaa8242fef24d7b6e08b7a6), the `contentobject_id` node column has been removed in favor of just `id`.

This fixes an issue with content cache clearing, by updating the column name.