Simplify new question form

In this form, the only case where `poll` might be present without
`question.poll` being present to is going to be the `new` action. We can
assign the poll in the `new` action and get rid of the `poll` variable
in the form.

app/components/admin/poll/questions/form_component.rb

@@ -1,10 +1,9 @@
 class Admin::Poll::Questions::FormComponent < ApplicationComponent
   include TranslatableFormHelper
   include GlobalizeHelper
-  attr_reader :poll, :question, :url
+  attr_reader :question, :url
 
-  def initialize(poll, question, url:)
-    @poll = poll
+  def initialize(question, url:)
     @question = question
     @url = url
   end