still some unneeded integer suffixes in the docs

[steveklabnik]

I noticed recently that the FFI chapter still has 1u32 in places, from before integer fallback existed. That, along with any other suffixes, should be removed.

(I'm not sure how many there are, exactly, but looking around for more while those get fixed is a Good Idea)

[friedm]

I'd be happy to take this, if no one minds.

[friedm]

Some suffixes are left in the chapters about casting, traits, and overloads but they all seemed helpful for the reader. There didn't seem to be any suffixes in the ffi chapter.

[nagisa]

May be closed?

[steveklabnik]

Thanks for doing that, @friedm