tr: different behavior than GNU with `echo "BB%t"|tr -c -d -s Bt "B" `

Playing with a pending tr fuzzer, it found this issue:
With GNU impl:
```
$ echo "BB%t"|/usr/bin/tr -c -d -s Bt "B"
Bt%
```

With our:
```
$ echo "BB%t"|tr -c -d -s Bt "B"
BBt%                                                 
```