You could probably also look into /home/hts/.hts/tvheadend/superuser, as that's the file that's supposed to be created (and re-created with dpkg-reconfigure) with the master login credentials. Stop tvh, rename that file, reconfigure, restart tvh, clear browser cache and connect.
Also, /home/hts/.hts/theadend/accesscontrol - you'll have a series of rules in here, each for a different set of permissions and users. The passwords are hashed, so you can't just change them, but you should be able to make them blank - or just change the permissions for existing users (ideally, the one you think you're connecting as), e.g, setting "webui": true and "admin": true, then re-connect. Again, tidy up afterwards unless you want that user to have these permissions.