remove self-reference in var_os doc

Co-authored-by: León Orell Valerian Liehr <me@fmease.dev>

Author: fleetingbytes

library/std/src/env.rs

@@ -242,7 +242,6 @@ fn _var(key: &OsStr) -> Result<String, VarError> {
 ///  - the environment variable's name contains
 /// the equal sign character (`=`) or the NUL character
 ///
-/// If this is not desired, consider using [`var_os`].
 ///
 /// Note that the method will not check if the environment variable
 /// is valid Unicode. If you want to have an error on invalid UTF-8,