Adjust wording for conciseness

Author: qxzcode

library/std/src/thread/local.rs

@@ -8,8 +8,8 @@ use crate::fmt;
 
 /// A thread local storage (TLS) key which owns its contents.
 ///
-/// This key uses the fastest possible implementation available to it for the
-/// target platform. It is instantiated with the [`thread_local!`] macro and the
+/// This key uses the fastest implementation available on the target platform.
+/// It is instantiated with the [`thread_local!`] macro and the
 /// primary method is the [`with`] method, though there are helpers to make
 /// working with [`Cell`] types easier.
 ///