I don't have the time to do this, but if you're rooter ... Google "delete sqlite row" then use something like this command (you must be rooted; if you don't have sqlite3 Google it):
sqlite3 /path/to/messaging/database.db "COMMAND"
Also, some versions I've encountered seem corrupted and fail without errors. You might want to try another one in that case.
I've linked my working version here, BTW:
https://groups.google.com/forum/#!topic/tasker/I-kpDEU3rsYMake sure you give it correct permissions.