Remove unused overlay value snapshots

docs/internal/overview.md

@@ -14,7 +14,8 @@ module and package documentation boundary. Its implemented public primitives are
   definitions, retains ordered claims and composite mapping origins, reports every
   conflicting location, and never aliases an input tree;
 - fixed selected-profile loading in `profile.go` and recursive, non-aliasing overlay
-  with displacement records in `overlay.go`;
+  with displacement records in `overlay.go`; overlay records retain origins,
+  while value explanation uses separate history applications;
 - detached parser-neutral CLI override validation and synthetic-source application
   in `override.go`, sharing overlay, source, byte, node, and depth policies;
 - a per-operation private reflection descriptor graph in `schema.go` for supported