[3.12] gh-108303: Remove `Lib/test/shadowed_super.py` (GH-114372) (#114433)

gh-108303: Remove `Lib/test/shadowed_super.py` (GH-114372)

Move code into Lib/test/test_super.py.
(cherry picked from commit 2ef520ebecf5544ba792266a5dbe4d53653a4a03)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>