Remove AI summaries and semantic searches

We were not using either. We can restore if we revisit.

script/migrations/backfill_weekly_summaries.rb

@@ -1,16 +0,0 @@
-#!/usr/bin/env ruby
-
-require_relative "../config/environment"
-
-WEEKS_TO_BACKFILL = 3
-
-ActiveRecord::Base.logger = Logger.new(File::NULL)
-
-ApplicationRecord.with_each_tenant do |tenant|
-  PeriodSummary.destroy_all
-  WEEKS_TO_BACKFILL.times do |index|
-    User.active.find_each do |user|
-      user.generate_weekly_summary(Time.current - index.weeks)
-    end
-  end
-end