Correct the comment about sorting of ACTIVE_FEATURES.

Author: nnethercote

compiler/rustc_feature/src/active.rs

@@ -148,8 +148,7 @@ macro_rules! declare_features {
 // was set. This is most important for knowing when a particular feature became
 // stable (active).
 //
-// Note that the features are grouped into internal/user-facing and then
-// sorted by version inside those groups. This is enforced with tidy.
+// Note that the features are sorted by name. This is enforced with tidy.
 //
 // N.B., `tools/tidy/src/features.rs` parses this information directly out of the
 // source, so take care when modifying it.