Reword "Internal Changes" to not say "no direct user facing benefits"

The "Internal Changes" section currently says "no direct user facing
benefits", but includes "significant improvements to the ... overall
performance", which is a user-facing benefit. Reword it to say "do not
affect any public interfaces" instead.

Author: joshtriplett

templates/relnotes.md

@@ -50,9 +50,9 @@ Compatibility Notes
 Internal Changes
 ----------------
 
-These changes provide no direct user facing benefits, but represent significant
-improvements to the internals and overall performance of rustc
-and related tools.
+These changes do not affect any public interfaces of Rust, but they represent
+significant improvements to the performance or internals of rustc and related
+tools.
 
 UNSORTED
 --------