Don't attempt to remove files that have already been removed

This is the likely cause of Phil's reported errors when removing files:
access=-110 info=smb_removefile name not found

The only way I was able to reproduce these errors was to attempt to remove the same file multiple times in the same file listing. In other worse, use 'R', remove a file, then 'P'revious back to the first file and try to remove it again. Or to remove it a file from the batch flag prompt and then attempt to remove it again. <shrug>