Rollup merge of #41019 - mandeep:fix-vec-swapremove-docs, r=BurntSushi

Fixed typo in doc comments for swap_remove

While reading the Vec docs, I came across the docs for swap_remove. I believe there is a typo in the comment and ```return``` should be ```returns```. This PR fixes this issue.

I also feel that the entire doc comment is a bit of a run-on and could be changed to something along the lines of ```Removes an element from anywhere in the vector and returns it. The vector is mutated and the removed element is replaced by the last element of the vector. ```

Thoughts?