CLN (PY2): Remove DataFrame/Series.timetuple
I was looking at the sphinx doc build warnings, and of them was complaining about the `DataFrame/Series.timetuple` attribute. This dummy `timetuple` attribute was added in https://github.com/pandas-dev/pandas/pull/24056, to fix comparison with `datetime.datetime`. 

Apart from the doc build problem (which can probably be fixed in another way as well), this also adds yet another (and for the rest useless / undocumented) attribute to our main classes.

But from a quick test (at least on linux with python 3.7, with Series) this is not needed to make it work. So removing again to see what travis/azure say.

@jbrockmendel do you remember the context of adding this?