[3.14] gh-140615: Update docstrings in the fcntl module (GH-140619) (GH-141231)

* Refer to bytes objects or bytes-like objects instead of strings.
* Remove backticks -- they do not have effect on formatting.
* Re-wrap lines to ensure the pydoc output fits in 80 columns.
(cherry picked from commit 610377056bad696915d70590429e68002bee9006)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>