smething along the lines of
/write -dl5 c:\info.txt

-d is for delete and l5 is the line number

you will need a way to stor the line number or you will have to scan the file for the line beginning with the nick you want to remove
something like //echo $read(help.txt, w, *help*)

you could perhaps use the $readn identifier which would give you the last line called using the $read but i am guessing that wuldnt work because you might write 3 names before you need to remove 1 ?