Remove tzinfo from datetime before writing cell with xlsxwriter
fixes #7056

see here: https://github.com/pydata/pandas/wiki

you need a test that fails w/o the fix and passes with
it will test in all excel engines

put in io/tests/test_excel.py (just copy the test format)
add the issue reference 
 @sboehler tests?
 Apologies, I don't think I will find the time to create tests, I guess I
should pull back the request.

2014-08-05 19:11 GMT+02:00 jreback notifications@github.com:

> @sboehler https://github.com/sboehler tests?
> 
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> Reply to this email directly or view it on GitHub
> https://github.com/pydata/pandas/pull/7060#issuecomment-51228638.
