chore: remove pre-rhino 1.8.0 warning

[radbasa]

• Closes #75

Description

• Remove one line in the how-to article for Rhino.
• Package version intentionally not updated.

Definition of Done

• [x] The change is thoroughly documented.
• [x] The CI passes (R CMD check, linter, unit tests, spelling).
• [x] Any generated files have been updated (e.g. .Rd files with roxygen2::roxygenise())

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.38%. Comparing base (2631943) to head (c2bb07b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #105 +/- ## ======================================= Coverage 98.38% 98.38% ======================================= Files 21 21 Lines 804 804 ======================================= Hits 791 791 Misses 13 13 ```

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