Revert "Allow apply_changes/1 to use nested schemaless changesets f…

…or `:map` type (#4516)"

This reverts commit a180048.

Closes #4520.

lib/ecto/changeset.ex

@@ -2190,9 +2190,6 @@ defmodule Ecto.Changeset do
   regardless if the changeset is valid or not. See `apply_action/2`
   for a similar function that ensures the changeset is valid.
 
-  If a field of type `:map` contains a schemaless changeset,
-  its changes too will be applied and returned as a map with atom keys.
-
   ## Examples
 
       iex> changeset = change(%Post{author: "bar"}, %{title: "foo"})
@@ -2211,9 +2208,6 @@ defmodule Ecto.Changeset do
         {:ok, {tag, relation}} when tag in @relations ->
           apply_relation_changes(acc, key, relation, value)
 
-        {:ok, :map} when is_struct(value, Changeset) ->
-          Map.put(acc, key, apply_changes(value))
-
         {:ok, _} ->
           Map.put(acc, key, value)
 

test/ecto/changeset_test.exs

@@ -1073,23 +1073,6 @@ defmodule Ecto.ChangesetTest do
     assert changed_post.category == nil
   end
 
-  test "apply_changes/1 with nested schemaless validation" do
-    params = %{"seo_metadata" => %{"keywords" => ["foo", "bar"], "slug" => "my-post-1"}}
-
-    changeset =
-      %Post{}
-      |> changeset(params)
-      |> update_change(:seo_metadata, fn seo_metadata ->
-        {%{}, %{keywords: {:array, :string}, slug: :string}}
-        |> cast(seo_metadata || %{}, [:keywords, :slug])
-        |> validate_required([:keywords, :slug])
-      end)
-
-    changed_post = apply_changes(changeset)
-
-    assert changed_post.seo_metadata == %{keywords: ["foo", "bar"], slug: "my-post-1"}
-  end
-
   describe "apply_action/2" do
     test "valid changeset" do
       post = %Post{}