These links are automaticaly generated by udev based on rules
found in /etc/udev/rules.d (though the location may be slightly different between distros, I'm not sure). You probably need to find the config file that contains this rule and modify it so that it doesn't create the symlinks.
Sorry if I can't give you any more detailed info on how to fix it, however. I've never had to deal with hard disk rules personally. I think the hard disk rules may be a bit more complex than most, and probably call external scripts to generate the device names.
It's strange that they should appear though. If the hdc device really isn't present on your system, then udev shouldn't be creating them in the first place. Has something about the hardware configuration been changed recently?
But in any case, you don't have to use /dev/cdrom. All you have to do is find the real device entry for your cdrom drive and use that instead.