Remove old static Window Functions page #13171

Part of #12740

Is your feature request related to a problem or challenge?

@Omega359 added the infrastructure to automatically create documentation from code in #12668

After #13161 Window Functions still have two pages

1. A "static" one: https://datafusion.apache.org/user-guide/sql/window_functions.html
2. A "auto generated" one https://datafusion.apache.org/user-guide/sql/window_functions_new.html

Describe the solution you'd like

Once all the window functions have all been migrated

• [Epic] Unify WindowFunction Interface (remove built in list of BuiltInWindowFunction s) #8709

We should remove the static window functions page (in favor of the auto generated one). We can follow the model of #13161

Describe alternatives you've considered

Basically this means for the scalar, window and aggregate functions:

1. Delete the static file docs/source/user-guide/sql/window_functions.md
2. Rename the _new files like docs/source/user-guide/sql/window_functions_new.md to docs/source/user-guide/sql/window_functions.md
3. Update the index page docs/source/user-guide/sql/index.rst to remove the _new entries
4. Update the script dev/update_function_docs.sh so it writes to the scalar_functions.md file

Additional context