delete weird fd_read feature

library/std/src/sys/net/connection/socket/windows.rs

@@ -451,7 +451,6 @@ impl Socket {
     }
 }
 
-#[unstable(reason = "not public", issue = "none", feature = "fd_read")]
 impl<'a> Read for &'a Socket {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         (**self).read(buf)

src/doc/unstable-book/src/library-features/fd-read.md

@@ -1,5 +0,0 @@
-# `fd_read`
-
-This feature is internal to the Rust compiler and is not intended for general use.
-
-------------------------