DOC: removed .value_counts() and .nunique() from the docs for 'table …
…methods available only for SeriesGroupBy' objects. GH46670

- [x] closes #46670 (Replace xxxx with the Github issue number)
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
thanks @TarunRKaushik 