For deleting a line from a file without open the file you can use sed.

For example, it has been very useful many times for me after anoying messages from ssh when a host I use to connect change the IP...

And sometimes you don't know the line number but you know a specific word from this line.

# delete the line 18 from '~/.ssh/known_hosts' file
sed -i '18 d' ~/.ssh/known_hosts
 
# also
sed -i 18d ~/.ssh/known_hosts
 
# delete few lines
# delete 6 lines from line 8
sed -i 8,+6d file.txt 
 
 
# delete the line where is 'TO DELETE'
sed -i '/TO DELETE/ d' file.txt