DOC: Clean-up references to v12 to v14 (both included)
- [ ] closes #xxxx
- [ ] tests added / passed
- [x ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

This is a continution of #17375 and cleans up references to old versions of pandas in the documentation.

Somme issues, I'd appreciate input on:
* In ``enhancingperf.rst`` there is under "Expression Evaluation via :func:`~pandas.eval` (Experimental)" and "The ``DataFrame.eval`` method (Experimental)" a line ``..versionadded:: 0.13``.
  In general I think it's a bit weird that something introduced back in 0.13 still is marked as experimental. I've let the versionadded stay for now, to somehow mark that ``eval`` is quite old even though it is experimental. Are there thoughts whether ``eval`` should still be marked experimental?