Update UDF notebook in User Guide. (#10668)

I noticed a couple lines I didn't expect in the UDF notebook in the User Guide while working on #10663. I didn't get these changes into that PR (had to wait for a local build to verify some things). The two changes are:
- We don't require `method="cudf"` in groupby statements.
- We don't need to execute `from cudf.utils import cudautils` to run this notebook.

(The cell execution counts also changed. There were some cells executed multiple times the last time this notebook was executed so they got out of order - this fixes it.)

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - https://github.com/brandon-b-miller

URL: #10668