conversation: remove unused users relationship

It is never used outside tests
and even there its correctness and/or
worth was questionable. The participations recipients
or just testing over the particiaptions’ user_id seem
like a better fit.
In particular this was always preloaded for API responses
needlessly slowing them down

lib/pleroma/conversation.ex

@@ -15,7 +15,6 @@ defmodule Pleroma.Conversation do
     # This is the context ap id.
     field(:ap_id, :string)
     has_many(:participations, Participation)
-    has_many(:users, through: [:participations, :user])
 
     timestamps()
   end

lib/pleroma/conversation/participation.ex

@@ -114,7 +114,7 @@ defmodule Pleroma.Conversation.Participation do
   def for_user_with_pagination(user, params \\ %{}) do
     from(p in __MODULE__,
       where: p.user_id == ^user.id,
-      preload: [conversation: [:users]]
+      preload: [:conversation]
     )
     |> restrict_recipients(user, params)
     |> select([p], %{id: p.last_bump, entry: p})

test/pleroma/conversation/participation_test.exs

@@ -202,10 +202,11 @@ defmodule Pleroma.Conversation.ParticipationTest do
     object3 = Pleroma.Object.normalize(activity_three, fetch: false)
 
     user = Repo.get(Pleroma.User, user.id)
+    participation_one = Pleroma.Repo.preload(participation_one, :recipients)
 
     assert participation_one.conversation.ap_id == object3.data["context"]
     assert participation_two.conversation.ap_id == object2.data["context"]
-    assert participation_one.conversation.users == [user]
+    assert participation_one.recipients == [user]
 
     # Pagination
     assert [%{id: pid, entry: participation_one}] =

test/pleroma/conversation_test.exs

@@ -119,7 +119,7 @@ defmodule Pleroma.ConversationTest do
 
     conversation_three =
       Conversation.get_for_ap_id(context)
-      |> Repo.preload([:participations, :users])
+      |> Repo.preload(participations: [:recipients])
 
     assert conversation_three.id == conversation.id
 
@@ -131,12 +131,11 @@ defmodule Pleroma.ConversationTest do
              tridi.id == user_id
            end)
 
-    assert Enum.find(conversation_three.users, fn %{id: user_id} ->
-             har.id == user_id
-           end)
+    expected_recipients = Enum.sort([har.id, tridi.id, jafnhar.id])
 
-    assert Enum.find(conversation_three.users, fn %{id: user_id} ->
-             tridi.id == user_id
+    assert Enum.all?(conversation_three.participations, fn %{recipients: recipients} ->
+             rids = Enum.map(recipients, & &1.id) |> Enum.sort()
+             assert rids == expected_recipients
            end)
   end