StealEmoji: drop superfluous basename

Since 3 commits ago we restrict shortcodes to a subset of
the POSIX Portable Filename Character Set, therefore
this can never have a directory component.

lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex

@@ -34,7 +34,6 @@ defp reject_emoji?({shortcode, _url}, installed_emoji) do
   end
 
   defp steal_emoji(%{} = response, {shortcode, extension}, emoji_dir_path) do
-    shortcode = Path.basename(shortcode)
     file_path = Path.join(emoji_dir_path, shortcode <> "." <> extension)
 
     case File.write(file_path, response.body) do