There should be no /dev/rsd4, the correct device nodes are /dev/rsd4a through /dev/rsd4p. As you've shown, the /dev/rsd4 file you have is not a device node anyway, it is a regular file.
You might want to take a look at its contents to try to understand what created it but it should be safe to just remove it. Most likely the file was created via a typo at some point. - todd
