remove type annotations from multiprocessing. (#129381)

* remove type annotations from multiprocessing.

One of them was technically invalid per typing specs... but since we're not
checking these in the stdlib today lets elide them.

https://discuss.python.org/t/static-type-annotations-in-cpython/65068/13

* use the actual comment style annotation format

Co-authored-by: 🇺🇦 Sviatoslav Sydorenko (Святослав Сидоренко) <wk.cvs.github@sydorenko.org.ua>

---------

Co-authored-by: 🇺🇦 Sviatoslav Sydorenko (Святослав Сидоренко) <wk.cvs.github@sydorenko.org.ua>