Remove some documentation duplicated between writeln! and write!

`writeln!` already includes a reference to `write!` for more
information, so remove duplicated information.

Author: joshtriplett

library/core/src/macros/mod.rs

@@ -526,25 +526,6 @@ macro_rules! write {
 ///     Ok(())
 /// }
 /// ```
-///
-/// A module can import both `std::fmt::Write` and `std::io::Write` and call `write!` on objects
-/// implementing either, as objects do not typically implement both. However, the module must
-/// import the traits qualified so their names do not conflict:
-///
-/// ```
-/// use std::fmt::Write as FmtWrite;
-/// use std::io::Write as IoWrite;
-///
-/// fn main() -> Result<(), Box<dyn std::error::Error>> {
-///     let mut s = String::new();
-///     let mut v = Vec::new();
-///
-///     writeln!(&mut s, "{} {}", "abc", 123)?; // uses fmt::Write::write_fmt
-///     writeln!(&mut v, "s = {:?}", s)?; // uses io::Write::write_fmt
-///     assert_eq!(v, b"s = \"abc 123\\n\"\n");
-///     Ok(())
-/// }
-/// ```
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "writeln_macro")]