Rollup merge of #33442 - tshepang:trim, r=steveklabnik

doc: trim some needless code

Author: GuillaumeGomez

src/libstd/io/mod.rs

@@ -182,11 +182,10 @@
 //!
 //! # fn foo() -> io::Result<()> {
 //! let f = try!(File::open("foo.txt"));
-//! let mut reader = BufReader::new(f);
+//! let reader = BufReader::new(f);
 //!
 //! for line in reader.lines() {
-//!     let line = try!(line);
-//!     println!("{}", line);
+//!     println!("{}", try!(line));
 //! }
 //!
 //! # Ok(())