Because else, py3_pickle3 tests fail e.g. as

        --- FAIL: TestFsDump/py3_pickle3/db=1 (0.00s)
            dump_test.go:70: fsdump: dump different:
                 Trans #00000 tid=0285cbac70a3d733 size=211 time=1979-01-03 21:00:26.400001 offset=117
                -    status='p' user=b'user0.12' description=b'step 0.12'
                +    status='p' user='user0.12' description='step 0.12'

        --- FAIL: TestFsDumpv/py3_pickle3/db=1 (0.00s)
            dump_test.go:70: fsdumpv: dump different:
                 ************************************************************
                -file identifier: b'FS30'
                +file identifier: 'FS30'

        ...

fs1tools/go sticks to py2 syntax because in my view it is more user
friendly. The preference of py2 or py3 syntax needs to be made anyway
because for fs1tools/go it is not possible to know beforehand to which
py kind its output will be compared against.

I think it is not very good for fstools/py output to be dependent on
python version. For the reference on this topic: output of zodbtools/py
is designed to be the same on both py2 and py3.