gh-95588: Drop the safety claim from `ast.literal_eval` docs. (GH-95919)

It was never really safe and this claim conflicts directly with the big warning in the docs about it being able to crash the interpreter.
(cherry picked from commit 8baef8ae367041a5cfefb40b19c7b87e9bcb56a2)

Co-authored-by: Gregory P. Smith <greg@krypto.org>