Revert "User.get_or_fetch_public_key_for_ap_id/1 is no longer required."

This reverts commit c0a50b7c3e.

test/pleroma/user_test.exs

@@ -1881,6 +1881,11 @@ defmodule Pleroma.UserTest do
     end
   end
 
+  test "get_or_fetch_public_key_for_ap_id fetches a user that's not in the db" do
+    assert {:ok, _key} =
+             User.get_or_fetch_public_key_for_ap_id("http://mastodon.example.org/users/admin")
+  end
+
   test "get_public_key_for_ap_id returns correctly for user that's not in the db" do
     assert :error = User.get_public_key_for_ap_id("http://mastodon.example.org/users/admin")
   end