Remove note on cohort-extractor docstrings

As spotted by @alschaffer in this issue:

#1573 (comment)

The relevant file has been edited just four times in the last two years,
and not since mid-2023.

Realistically, the only people who might make small updates to
cohort-extractor are likely to be developers now, and this note probably
just mystifies anyone else who encounters it.

docs/updating-the-docs.md

@@ -26,24 +26,3 @@ It may take a few seconds for changes you make to appear.
 When adding or revising text, use [Semantic Line Breaks](https://sembr.org/) rather than fixed length lines.
 With semantic line breaks, the diff is more concise and easier to interpret than with fixed length lines,
 where a single change can propagate through a whole paragraph.
-
-## Making changes to the study definition variables
-
-Edit the docstrings in the [`patients.py` file in the `cohort-extractor` repository](https://github.com/opensafely-core/cohort-extractor/blob/master/cohortextractor/patients.py).
-
-!!! note "Variable docstrings follow the [Google style guide](https://google.github.io/styleguide/pyguide.html#383-functions-and-methods)."
-
-If you don't have write access, you can fork the cohort-extractor repo, make a change, and submit a pull request.
-Editing directly in GitHub will take you through these steps automatically.
-At least one commit in the pull request should be named using the prefix `fix: ` or `feature: `. For example `fix: typo in age_as_of docstring`.
-This ensures that a new version of `cohortextractor` is released and can be imported by the documentation via GitHub actions.
-Then add a reference to your new variable in the [variables page](legacy/study-def-variables.md).
-
-Additionally, the
-[`requirements.prod.txt`](https://github.com/opensafely/documentation/blob/main/requirements.prod.txt)
-file in the [documentation
-repo](https://github.com/opensafely/documentation) itself has to be
-updated to match the new incremented version of `cohortextractor`. See
-the [documentation repository's
-README](https://github.com/opensafely/documentation#building-locally-and-testing)
-that details the use of `pip-compile` for this.