AFIAK, it's fine to leave the user/pw of the "worker" there, as that's only what connects to the pool and has no transacting abilities... it actually behooves you too, as if someone were to connect; they would be helping you mine. Either way, I admire your willingness to remove the login/pw - many don't.
Now onto your issue.
I had the same problem, have you tried installing
libidn through
MacPorts?
If you use homebrew, it's likely just using the wrong directory and you can modify them as seen
here.
Hope this helps.
When I try that code linked from your post, I get permission denied from the first line of code, and this message from the second line of code:
ln: /usr/local/Cellar/libidn/1.23/lib/libidn.11.dylib: No such file or directory
I'm really confused. I only just downloaded homebrew, and the Command Line Tool for xcode. I'm pretty new to this. Do I have to download ruby as well? I am pretty sure I installed libidn. Still, I get the same messages as in the OP.