doc: remove misleading/confusing info

We have to specify the module and the function name in the example where
the module shares a crate with the executable as well, so remove the
redundant (and potentially confusing) mention.
auto merge of #16724 : tshepang/rust/misleading, r=brson

We have to specify the module and the function name in the example where
the module shares a crate with the executable as well, so remove the
redundant (and potentially confusing) mention.