OS Extension traits have confusing available-on annotation #144681
Description
Many extension traits for Linux show the requirements as:
Available on Linux and (Linux or Android) only.
It would be much less confusing if they just said "Available on Linux only."
This is happening because behind the scenes, the std::os::linux and std::os::android modules re-export the same underlying traits. However, the traits are only re-exported under the std::os::linux module on target_os="linux", so the docs for the item in std::os::linux should not talk about Android.
(There is no equivalent issue for target_os="android" because the traits are not displayed at all in the documentation on Android.)