Remove unused method

This method was not used since commit d0245059.

app/models/geozone.rb

@@ -13,10 +13,6 @@ class Geozone < ApplicationRecord
     Geozone.pluck(:name)
   end
 
-  def self.city
-    where(name: "city").first
-  end
-
   def safe_to_destroy?
     Geozone.reflect_on_all_associations(:has_many).all? do |association|
       association.klass.where(geozone: self).empty?