C++: Reinstate accidentally-deleted commend

cpp/ql/src/Best Practices/Unused Entities/UnusedLocals.ql

@@ -56,6 +56,6 @@ where
   not exists(DeclStmt ds | ds.getADeclaration() = v and ds.isInMacroExpansion()) and // variable declared in a macro expansion
   not declarationHasSideEffects(v) and
   not exists(AsmStmt s | f = s.getEnclosingFunction()) and
-  not v.getAnAttribute().getName() = "unused" and
+  not v.getAnAttribute().getName() = "unused" and // unextracted expr may use `v`
   not f.hasErrors()
 select v, "Variable " + v.getName() + " is not used."