Move RecursivelyEnumeratedSet_forest code to sage/sets/recursively_enumerated_set.pyx, remove deprecated classes SearchForest, TransitiveIdeal, TransitiveIdealGraded #16351
Description
Move the code of SearchForest from sage/combinat/backtrack.py to sage/sets/recursively_enumerated_set.pyx into a class named RecursivelyEnumeratedSet_forest.
This is a follow up of #6637.
Component: combinatorics
Author: Matthias Koeppe
Branch: 908acba
Reviewer: Vincent Delecroix
Issue created by migration from https://trac.sagemath.org/ticket/16351