DOC: Update DataFrame.sparse methods' docstring to pass docstring validation
- [ ] xref #58065

Fixed docstring errors for:

`pandas.DataFrame.sparse`
`pandas.DataFrame.sparse.density`
`pandas.DataFrame.sparse.from_spmatrix`
`pandas.DataFrame.sparse.to_coo`
`pandas.DataFrame.sparse.to_dense`

Fixed functions also removed from code_checks.sh
Thanks @gboeker 