Remove NotImplementedError for parse_dates keyword in read_excel
Rebase and update of PR https://github.com/pydata/pandas/pull/12051

lgtm.
 Apparently it does not work out of the box anymore by re-enabling it (probably due to changes in `PythonParser` over the last year), so will have to take a deeper look
 @jorisvandenbossche ? @jorisvandenbossche let's update and get this in. @jorisvandenbossche can you update @jorisvandenbossche can you rebase