use existing inflections instead of custom helper (#4624)

* use existing inflections instead of custom helper

* use ActiveSupport versions

app/helpers/account_helper.rb

@@ -1,14 +0,0 @@
-# frozen_string_literal: true
-
-module AccountHelper
-  def protocol_for_display(protocol)
-    case protocol
-    when 'activitypub'
-      'ActivityPub'
-    when 'ostatus'
-      'OStatus'
-    else
-      protocol
-    end
-  end
-end