activity: when restricting deactivated users, precalculate the user list

the PostgreSQL query planner is easily confused due to the complexity of
certain queries we make.  while we plan to simplify these queries through
unification of activities and objects, we are not yet there.  it has been
discovered that using a precalculated list of deactivated users encourages
the query planner to prefer simpler indices instead of the
activity_visibility index.

accordingly, drop the subquery and precalc the user list instead.

lib/pleroma/activity.ex

@@ -362,12 +362,12 @@ def query_by_actor(actor) do
   end
 
   def restrict_deactivated_users(query) do
+    deactivated_users =
+      from(u in User.Query.build(deactivated: true), select: u.ap_id)
+      |> Repo.all()
+
     from(activity in query,
-      where:
+      where: activity.actor not in ^deactivated_users
-        fragment(
-          "? not in (SELECT ap_id FROM users WHERE info->'deactivated' @> 'true')",
-          activity.actor
-        )
     )
   end