The doc build still fails with

/home/circleci/project/doc/api/prev_api_changes/api_changes_1.4.x.rst:152: WARNING: py:obj reference target not found: tight_bbox.adjust_bbox
/home/circleci/project/doc/api/prev_api_changes/api_changes_1.4.x.rst:152: WARNING: py:obj reference target not found: tight_bbox.process_figure_for_rasterizing
/home/circleci/project/doc/api/prev_api_changes/api_changes_2.2.0.rst:162: WARNING: py:obj reference target not found: tight_layout.auto_adjust_subplotpars
/home/circleci/project/doc/api/prev_api_changes/api_changes_3.0.1.rst:4: WARNING: py:obj reference target not found: tight_layout.auto_adjust_subplotpars
/home/circleci/project/doc/api/prev_api_changes/api_changes_3.0.1.rst:4: WARNING: py:obj reference target not found: tight_layout.get_tight_layout_figure

These historic API change notes reference the now non-public API. The way to handle this is to change the links to verbatim as that API is no longer public and available in the docs. E.g. for the first one, change

`.tight_bbox.adjust_bbox`

to

``matplotlib.tight_bbox.adjust_bbox``

It just occured to me that we can an should keep the history for git blame. If you create a new _tight_bbox.py, copy everything over and add the stub in tight_bbox.py, then all of _tight_bbox.py will be marked as your change and not have any history behind that.

To preserve the history:

1. git mv tight_bbox.py _tight_bbox.py and put this into a commit.
2. Create a new tight_bbox.py with the deprecation and put this into a second commit.

It's important that the move is in a separate commit. Otherwise git assumes you created _tight_bbox.py and modified tight_bbox.py. However, you can have the moves of both files in one commit and both deprecations in the second.

Sorry to bring this in at a quite late review stage, but it's really important for us to be able to easily dig into the code history.