CLN: Remove tupleize_cols keyword in io methods; from_csv method
- [x] xref #6581
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Removes:

- `tupleize_cols` keyword in `read_html`, `read_csv`, `to_csv`
- `DataFrame/Series.from_csv`