Here's how I deleted a bunch of spam links added by the user 'seekgzl' in one go:

 cd /group/project/proofgeneral/data/trac-project-env/db/
 sqlite3 trac.db
 delete from ticket_change where author='seekgzl';

The ​TicketDeletePlugin is supposed to provide an interface to help delete tickets or ticket changes, but my attempt to install it didn't work.