tr -d should reject a second argument

```
echo "5"|/usr/bin/tr -d "c" "p"
/usr/bin/tr: extra operand 'p'
Only one string may be given when deleting without squeezing repeats.
Try '/usr/bin/tr --help' for more information.
```

```
$ echo "5"|../target/debug/coreutils tr -d "c" "p"
5
```


Found by fuzzing it