Remove redundant by_question grouping in Admin::Poll::Results::QuestionComponent

Stop grouping partial results by question_id inside the component.

Note that group_by on an empty collection already returns
an empty hash, so the previous "|| {}" is not needed.

app/components/admin/poll/results/question_component.rb

@@ -7,12 +7,6 @@ class Admin::Poll::Results::QuestionComponent < ApplicationComponent
   end
 
   def by_answer
-    @by_answer ||= by_question[question.id].present? ? by_question[question.id].group_by(&:answer) : {}
+    @by_answer ||= partial_results.where(question: question).group_by(&:answer)
   end
-
-  private
-
-    def by_question
-      @by_question ||= partial_results.group_by(&:question_id)
-    end
 end