Remove docs needed only for pytest-notebook

Author: awf

BUILDING.md

@@ -7,13 +7,6 @@ pip install -e .
 ( cd docs && make html )
 ```
 
-If notebook outputs have changed, then verify the new outputs are correct, and run
-```
-pytest --nb-force-regen
-```
-If a notebook has volatile outputs (e.g. timings), see the `nbreg/diff_replace` metadata in `04-benchmark.ipynb` for an example of how to selectively ignore it.
-
-
 #### Pushing
 ```
 sh etc/package.sh