one quick way.
Use ttool to decompile the trafficxxxx.bgl file.
You should have flight plan file, aircraft file...
import the flight plan file into excel (use csv to seperate into different column).
So your excel file may look like this.
col 1 col 2......
#4 (can't remember what's next)
Now, all you have to do is to sort the column with ac#.
select and delete all flight plan associated with that ac#. save the file as text file.
recompile and you are done.