[Announcements] Unlink transparency mode and monthly announcements (#11945)

## Summary of the problem
<!-- Why are these changes being made? What problem does it solve? Link
any related issues to provide more details. -->
See #11944 for context - for now, we've decided to not automatically
link transparency mode to enabling monthly announcements as it doesn't
give the event managers any chance to get context on what monthly
announcements are.

## Describe your changes
<!-- Explain your thought process to the solution and provide a quick
summary of the changes. -->
Remove the callbacks on `Event::Configuration` and `Event` that
automatically enabled monthly announcements if the event was/became
transparent.

<!-- If there are any visual changes, please attach images, videos, or
gifs. -->

Author: polypixeldev

app/models/event.rb

@@ -451,7 +451,6 @@ def ancestor_organizer_positions
   after_validation :move_friendly_id_error_to_slug
 
   after_update :generate_stripe_card_designs, if: -> { attachment_changes["stripe_card_logo"].present? && stripe_card_logo.attached? && !Rails.env.test? }
-  before_save :enable_monthly_announcements
 
   # We can't do this through a normal dependent: :destroy since ActiveRecord does not support deleting records through indirect has_many associations
   # https://github.com/rails/rails/commit/05bcb8cecc8573f28ad080839233b4bb9ace07be
@@ -969,13 +968,6 @@ def enforce_transparency_eligibility
     end
   end
 
-  def enable_monthly_announcements
-    # We'll enable monthly announcements when transparency mode is turned on
-    if is_public_changed?(to: true)
-      config.update(generate_monthly_announcement: true)
-    end
-  end
-
   def stripe_transaction_merchant(transaction)
     merchant_data = transaction.stripe_transaction["merchant_data"]
     yp_merchant = YellowPages::Merchant.lookup(network_id: merchant_data["network_id"])

app/models/event/configuration.rb

@@ -29,15 +29,10 @@ class Configuration < ApplicationRecord
     normalizes :contact_email, with: ->(contact_email) { contact_email.strip.downcase }
     validates :subevent_plan, inclusion: { in: -> { Event::Plan.available_plans.map(&:name) } }, allow_blank: true
 
-    before_create :set_defaults
     after_save :create_or_destroy_monthly_announcement
 
     private
 
-    def set_defaults
-      self.generate_monthly_announcement = event.is_public if self.generate_monthly_announcement.nil?
-    end
-
     def create_or_destroy_monthly_announcement
       if self.generate_monthly_announcement_previously_changed?
         if self.generate_monthly_announcement