docs: rust: remove spurious item in `expect` list

This list started as a "when to prefer `expect`" list, but at some point
during writing I changed it to a "prefer `expect` unless..." one. However,
the first bullet remained, which does not make sense anymore.

Thus remove it. In addition, fix nearby typo.

Fixes: 04866494 ("Documentation: rust: discuss `#[expect(...)]` in the guidelines")
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20241117133127.473937-1-ojeda@kernel.org


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>