read_excel interprets date columns as datetimes despite parse_dates = False

[lucasgautheron]

Not a bug, for the following reasons:

• read_excel does not attempt to parse strings as dates w/ parse_dates = False, but it treats date/time cells as datetime objects instead
• it should be assumed that the format specified in the documentation is standard and does not require special treatments across datasets
• therefore, the datasets using excels as an index should not use date/time cells. the problem can also avoided using CSV
• if the problem occurs, the dataset should be fixed in order to pass the validation. this way, the index can be read flawlessly w/o requiring any sort of additional treatment