Update protobuf converter for italian_leading_zero behaviour
Update protobuf converter for italian_leading_zero behaviour

Commit b1be9e7cb18791ff4 changed italian_leading_zero to be 
more consistent with upstream, by having 3 states (None, False, True).

Remove the special case code in the protobuf converter that dealt
with the old 2 state version.
daviddrysdale/python-phonenumbers,shikigit/python-phonenumbers,dongguangming/python-phonenumbers,roubert/python-phonenumbers,titansgroup/python-phonenumbers,daviddrysdale/python-phonenumbers,SergiuMir/python-phonenumbers,daviddrysdale/python-phonenumbers,agentr13/python-phonenumbers,gencer/python-phonenumbers,daodaoliang/python-phonenumbers