chore: drop red-black map/tree entries from overview.yaml

`Batteries.RBMap` and `Batteries.RBSet` were removed by the batteries
recycling refactor (leanprover-community/batteries#1792, leanprover-community#1793; the
`Batteries.Data.RBMap.Basic` module is now a deprecated_module
recommending `Std.TreeMap`). They no longer exist under those names, so
`lake exe check-yaml` rejected the stale `docs/overview.yaml` entries.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: kim-em

docs/overview.yaml

@@ -583,14 +583,12 @@ Data structures:
 
   Maps:
     key-value map: 'AList'
-    red-black map: 'Batteries.RBMap'
     hash map: 'Std.HashMap'
     finitely supported function: 'Finsupp'
     finite map: 'Finmap'
 
   Trees:
     tree: 'Tree'
-    red-black tree: 'Batteries.RBSet'
     size-balanced binary search tree: 'Ordnode'
     W type: 'WType'