chore: use associations for finding workshop sponsors with hosts

I have implemented workshop associations' hosts to be returned by the host method and I've removed the scope to do the same on the workshop_sponsor model

Author: davidmillen50

app/models/workshop.rb

@@ -30,8 +30,14 @@ class Workshop < ApplicationRecord
   before_validation :set_date_and_time, :set_end_date_and_time, if: proc { |model| model.chapter_id.present? }
   before_validation :set_opens_at
 
+  def self.workshop_sponsors_with_host_true
+    includes(:workshop_sponsors).flat_map do |workshop|
+      workshop.workshop_sponsors.select { |ws| ws.host == true }
+    end
+  end
+
   def host
-    WorkshopSponsor.hosts.for_workshop(id).first&.sponsor
+    Workshop.workshop_sponsors_with_host_true.first&.sponsor
   end
 
   def waiting_list

spec/models/workshop_sponsor_spec.rb

@@ -19,18 +19,5 @@
         expect(WorkshopSponsor.hosts).to eq []
       end
     end
-
-    context '#for_workshop' do
-      it 'includes sponsors of the workshop' do
-        workshop_sponsor = Fabricate(:workshop_sponsor)
-        expect(WorkshopSponsor.for_workshop(workshop_sponsor.workshop)).to include(workshop_sponsor)
-      end
-
-      it 'excludes sponsors not sponsoring the workshop' do
-        Fabricate(:workshop_sponsor)
-        workshop = Fabricate(:workshop_no_sponsor)
-        expect(WorkshopSponsor.for_workshop(workshop)).to eq []
-      end
-    end
   end
 end