Revert "Merge pull request #19755 from yuki24/activerecord/support-for-set"

This reverts commit 524d4059, reversing
changes made to 34d3a609.

Reasoning behind the revert are in the PR discussion:
https://github.com/rails/rails/pull/19755

- This means that types can no longer cast to/from `Set`, and reasonably
  work with `where` (we already have this problem for `array`/`json`
  types on pg)
- This adds precedent for every other `Enumerable`, and we can't target
  `Enumerable` directly.
- Calling `to_a` on a `Set` is reasonable.

activerecord/CHANGELOG.md

-*   Add support for `Set` to `Relation#where`.
-
-    *Yuki Nishijima*
-
 *   Fixed a bug where uniqueness validations would error on out of range values,
     even if an validation should have prevented it from hitting the database.
 

activerecord/lib/active_record/relation/predicate_builder.rb

@@ -20,7 +20,6 @@ def initialize(table)
       register_handler(Range, RangeHandler.new(self))
       register_handler(Relation, RelationHandler.new)
       register_handler(Array, ArrayHandler.new(self))
-      register_handler(Set, ArrayHandler.new(self))
       register_handler(AssociationQueryValue, AssociationQueryHandler.new(self))
     end
 

activerecord/test/cases/relations_test.rb

@@ -848,16 +848,6 @@ def test_find_all_using_where_with_relation_with_select_to_build_subquery
     }
   end
 
-  def test_find_all_using_where_with_a_set
-    david = authors(:david)
-    mary  = authors(:mary)
-    set   = Set.new([david.id, mary.id])
-
-    assert_queries(1) {
-      assert_equal [david, mary], Author.where(id: set).to_a
-    }
-  end
-
   def test_exists
     davids = Author.where(:name => 'David')
     assert davids.exists?