Destroy some cdata

def _destroy(cls, cdata):
        """Destroy some cdata"""
        # Leptonica API uses double-pointers for its destroy APIs to prevent
        # dangling pointers. This means we need to put our single pointer,
        # cdata, in a temporary CDATA**.
        pp = ffi.new('{} **'.format(cls.LEPTONICA_TYPENAME), cdata)
        cls.cdata_destroy(pp)