Error when uninstalling trusted contacts

I disabled the module trusted_contacts, but when I went to uninstall it to clear the database, the following was logged in the apache error log:

PHP Fatal error: Call to undefined function variable_delete() in /path/to/docroot/profiles/commons/modules/commons/commons_trusted_contacts/commons_trusted_contacts.install on line 54

This suggests that there is a link between trusted_contacts and variable that is not fully documented/enforced.

Note that this site does not have variable enabled.

The connection is not as simple as having trusted_contacts depend on variable, as variable would have been disabled/uninstalled before trusted_contacts which leaves the problem unsolved.