Detail `del s[i:j]` in `Mutable Sequence Types`

# Documentation

In [Mutable Sequence Types](https://docs.python.org/3.15/library/stdtypes.html#mutable-sequence-types):
The description of `del s[i:j]` is "same as s[i:j] = []". This is not clear enough.

We should make it consistent with `del s[i:j:k]` ("removes the elements of s[i:j:k] from the list").





### Linked PRs
* gh-134834