ActivityPub: Use is_unicode_emoji? function.

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -315,7 +315,7 @@ def update(%{to: to, cc: cc, actor: actor, object: object} = params) do
   def react_with_emoji(user, object, emoji, options \\ []) do
     with local <- Keyword.get(options, :local, true),
          activity_id <- Keyword.get(options, :activity_id, nil),
-         is_emoji?(emoji),
+         Pleroma.Emoji.is_unicode_emoji?(emoji),
          reaction_data <- make_emoji_reaction_data(user, object, emoji, activity_id),
          {:ok, activity} <- insert(reaction_data, local),
          {:ok, object} <- add_emoji_reaction_to_object(activity, object) do

lib/pleroma/web/activity_pub/utils.ex

@@ -277,10 +277,6 @@ def get_object_likes(%{data: %{"id" => id}}) do
     |> Repo.all()
   end
 
-  def is_emoji?(emoji) do
-    String.length(emoji) == 1
-  end
-
   def make_emoji_reaction_data(user, object, emoji, activity_id) do
     make_like_data(user, object, activity_id)
     |> Map.put("type", "EmojiReaction")

test/web/pleroma_api/pleroma_api_controller_test.exs

@@ -8,7 +8,6 @@ defmodule Pleroma.Web.PleromaAPI.PleromaAPIControllerTest do
   alias Pleroma.Conversation.Participation
   alias Pleroma.Repo
   alias Pleroma.Web.CommonAPI
-  alias Pleroma.Web.MastodonAPI.AccountView
 
   import Pleroma.Factory