A company that provided the now-defunct website Backpage with computer software is not responsible for the damages allegedly suffered by an underage girl featured in an ad on the site’s “Escort Page,” a federal judge held Monday.In a written opinion, U.S. District Judge Andrea R. Wood of the Northern District of Illinois dismissed with prejudice a lawsuit filed by “G.G.” and her mother accusing Salesforce.com Inc. of violating sex-trafficking laws.The mother and daughter allege Salesforce benefited financially by selling …