[3.12] Docs: Remove the numbered steps from the Argument Clinic tutorial (GH-107203) (#107317)

Instead, order the tutorial as one body of prose, making it easier to
align the tutorial according to Diátaxis principles.

(cherry picked from commit 592395577c679543d899e68a3cff538b8b4df80d)

Co-authored-by: Erlend E. Aasland <erlend@python.org>