A2 fast path not working with Tone3000 models

[mikeoliphant]

The A2 fast path code is looking for a head_scale of 0.01 when validating a config. This does not seem to be true of the A2 models trained on Tone3000, so the fast path is being bypassed.

[mikeoliphant]

The fast path code seems to be using the head_scale value from the model, so I'm not sure why that check is there. Removing the check enables the fast path on the Tone3000 models.