DOC:fix of DOCUMENTATION
- [ ] closes #38311
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ Timedelta.isoformat DOC had duplicates i have deleted one of them. And their was two lines with wrong output that i have also fixed.] whatsnew entry
