Deactivate local users on deletion instead of deleting the record

Prevents the possibility of re-registration, which allowed to read
DMs of the deleted account.

Also includes a migration that tries to find any already deleted
accounts and insert skeletons for them.

Closes pleroma/pleroma#1687

test/tasks/user_test.exs

@@ -92,7 +92,7 @@ defmodule Mix.Tasks.Pleroma.UserTest do
       assert_received {:mix_shell, :info, [message]}
       assert message =~ " deleted"
 
-      refute User.get_by_nickname(user.nickname)
+      assert %{deactivated: true} = User.get_by_nickname(user.nickname)
     end
 
     test "no user to delete" do

test/user_test.exs

@@ -1135,16 +1135,7 @@ defmodule Pleroma.UserTest do
       refute Activity.get_by_id(activity.id)
     end
 
-    test "it deletes deactivated user" do
-      {:ok, user} = insert(:user, deactivated: true) |> User.set_cache()
-
-      {:ok, job} = User.delete(user)
-      {:ok, _user} = ObanHelpers.perform(job)
-
-      refute User.get_by_id(user.id)
-    end
-
-    test "it deletes a user, all follow relationships and all activities", %{user: user} do
+    test "it deactivates a user, all follow relationships and all activities", %{user: user} do
       follower = insert(:user)
       {:ok, follower} = User.follow(follower, user)
 
@@ -1164,8 +1155,7 @@ defmodule Pleroma.UserTest do
       follower = User.get_cached_by_id(follower.id)
 
       refute User.following?(follower, user)
-      refute User.get_by_id(user.id)
-      assert {:ok, nil} == Cachex.get(:user_cache, "ap_id:#{user.ap_id}")
+      assert %{deactivated: true} = User.get_by_id(user.id)
 
       user_activities =
         user.ap_id

test/web/activity_pub/transmogrifier_test.exs

@@ -872,7 +872,8 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
 
     @tag capture_log: true
     test "it works for incoming user deletes" do
-      %{ap_id: ap_id} = insert(:user, ap_id: "http://mastodon.example.org/users/admin")
+      %{ap_id: ap_id} =
+        insert(:user, ap_id: "http://mastodon.example.org/users/admin", local: false)
 
       data =
         File.read!("test/fixtures/mastodon-delete-user.json")