[3.12] gh-111726: Remove some doctests from sqlite3 docs (GH-117623) (#117625)

* remove load extension doctest since we cannot skip it conditionally
* remove sys.unraisablehook example; using unraisable hooks is not "an
  improved debug experience"

(cherry picked from commit e338e1a4ec5e43a02447f4ec80320d7fc12b3ed4)

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