Apply suggestions from code review

Co-authored-by: Michael Goulet <michael@errs.io>

Author: saethlin

compiler/rustc_middle/src/ty/sty.rs

@@ -1864,8 +1864,8 @@ impl<'tcx> Ty<'tcx> {
             // Definitely absolutely not copy.
             ty::Ref(_, _, hir::Mutability::Mut) => false,
 
-            // The library has a blanket Copy impl for shared references and raw pointers,
-            // regardless of metadata.
+            // The standard library has a blanket Copy impl for shared references and raw pointers,
+            // for all unsized types.
             ty::Ref(_, _, hir::Mutability::Not) | ty::RawPtr(..) => true,
 
             ty::Coroutine(..) | ty::CoroutineWitness(..) => false,