Remove unused by_geozone_id scope from Poll

The "by_geozone_id" scope in Poll is no longer used anywhere in the code.
It was first introduced in commit 20cb044015 ("adds search and filter
for poll questions") and later moved to the Poll model in commit
d024505960 ("moves geozones from poll question to poll in models"),
but has never been referenced since.

app/models/poll.rb

@@ -71,7 +71,6 @@ class Poll < ApplicationRecord
   scope :expired, -> { where(ends_at: ...Time.current) }
   scope :recounting, -> { where(ends_at: (RECOUNT_DURATION.ago)...Time.current) }
   scope :published, -> { where(published: true) }
-  scope :by_geozone_id, ->(geozone_id) { where(geozones: { id: geozone_id }.joins(:geozones)) }
   scope :public_for_api, -> { all }
   scope :not_budget, -> { where(budget_id: nil) }
   scope :created_by_admin, -> { where(related_type: nil) }