rust: page: remove unnecessary helper function from doctest

rust: page: remove unnecessary helper function from doctest

Doctests in `page.rs` contained a helper function `dox` which acted
as a wrapper for using the `?` operator. However, this is not needed
because doctests are implicitly wrapped in function see [1].

Link: https://doc.rust-lang.org/rustdoc/write-documentation/documentation-tests.html#using--in-doc-tests
Suggested-by: Dirk Behme <dirk.behme@de.bosch.com>
Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://lore.kernel.org/rust-for-linux/459782fe-afca-4fe6-8ffb-ba7c7886de0a@de.bosch.com/
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Daniel Sedlak <daniel@sedlak.dev>
Link: https://lore.kernel.org/r/20241123095033.41240-4-daniel@sedlak.dev
[ Fixed typo in SoB. Slightly reworded commit. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>