trellis: remove import of fsm_utils from __init__.py for gr-trellis.

fsm_utils uses scipy, which is not a required dependency. Adding this to the trellis import then won't work if you don't have scipy.

These imports work:
from gnuradio.trellis.fsm_utils as fu
from gnuradio.trells import fsm_utils

This will not:
from gnuradio import trellis
trellis.fsm_utils.*