DOC: fix doc errors from removing datetime-like Series ops

[jreback]

http://pandas-docs.github.io/pandas-docs-travis/timeseries.html#custom-business-days-experimental
http://pandas-docs.github.io/pandas-docs-travis/whatsnew.html#experimental-features

[jorisvandenbossche]

another: in the api.rst doc section remove all Series entries for this