DOC: Fix introduction of DataFrame.rename
- [x] closes #43708
- [ ] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

there is a discussion somewhere, that `inplace` is considered being deprecated becuase it doesn't really perform the calculation in place (and therefore save memory) it actually creates a copy and disregards it. Therefore the original docs  here are actually more informative than what you have changed it to. closing as this change makes the docs different that all other functions where this arg is.