server : avoid antiprompt in probabilities of final response

[jhen0409]

This fix the probabilities of stopping_word are included in the final response of /completion.

To test response without stream mode:

curl --url http://localhost:8080/completion --header "Content-Type: application/json" \
  --data '{ "n_probs": 1, "prompt": "Hello my name is", "stop": ["I"] }' | json_pp

With stream mode (see the last event):

curl -N --url http://localhost:8080/completion --header "Content-Type: application/json" \
  --data '{ "stream": true, "n_probs": 1, "prompt": "Hello my name is", "stop": ["I"] }'

Or see the console output in the web UI.

[SlyEcho]

Yep, that does the trick.