Remove it just like you would any other file: rm /usr/lib/libmysqlclient.18.dylib. rm will remove the symlink itself, not the file the link is pointing at.
I had a link pointing to a folder with short-name "testproject":
you make that with this command
ln -s /Users/SHERIF/repo/test testproject
I had to change the folder name to something else for some reasons when I run the command unlink pointing to the old folder directory it didn't work.
I tried to only unlink testproject to remove the short-name so I can re-use the same name again and link to the newly named folder. it did work fine for me.
Somehow I had a symlink to a non-existing folder. Have no idea how it happened but to remove it I found the easiest way was open in finder and manually delete it. I came to this decision after an hour wasted on trying to delete it with the Terminal.