Remove unused artist functionality

lib/music_library_web/controllers/artist_controller.ex

@@ -1,27 +0,0 @@
-defmodule MusicLibraryWeb.ArtistController do
-  use MusicLibraryWeb, :controller
-
-  alias MusicLibrary.Artists
-  alias MusicLibrary.Assets.Transform
-  alias MusicLibraryWeb.AssetController
-
-  def image(conn, %{"musicbrainz_id" => artist_id}) do
-    case Artists.get_image(artist_id) do
-      nil ->
-        not_found(conn)
-
-      %{image_data_hash: hash} ->
-        payload =
-          %Transform{hash: hash}
-          |> Transform.encode!()
-
-        AssetController.show(conn, %{"transform_payload" => payload})
-    end
-  end
-
-  defp not_found(conn) do
-    conn
-    |> put_status(:not_found)
-    |> text("Not found")
-  end
-end