tee: remove unused returned usize

[oech3]

No description provided.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/cp/link-heap is now being skipped but was previously passing.
Congrats! The gnu test tests/basenc/bounded-memory is now passing!

[sylvestre]

i am surprised that the compiler or clippy didn't find it

[oech3]

Maybe, rustc and clippy considers usize is used at _ of _ => Ok(()),.

[cakebaker]

Thanks!