Remove bytes in calls to str.split()

It is useless to write foo.split(b'bar') rather than foo.split(bar). In Python
2, this is exactly the same thing:

    >>> 'fooXbar'.split('X')
    ['foo', 'bar']
    >>> 'fooXbar'.split(b'X')
    ['foo', 'bar']

In Python 3, using bytes in split() is an error:

    >>> 'fooXbar'.split('X')
    ['foo', 'bar']
    >>> 'fooXbar'.split(b'X')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: Can't convert 'bytes' object to str implicitly