Chore: remove unused scopes on workshop_sponsor model

These scopes have been replaced by the new query so they're not needed and neither are the tests

Author: davidmillen50

app/models/workshop_sponsor.rb

@@ -3,7 +3,4 @@ class WorkshopSponsor < ApplicationRecord
   belongs_to :workshop
 
   validates :sponsor_id, uniqueness: { scope: :workshop_id, message: :already_sponsoring }
-
-  scope :hosts, -> { where('workshop_sponsors.host = ?', true) }
-  scope :for_workshop, ->(workshop_id) { where('workshop_sponsors.workshop_id = ?', workshop_id) }
 end

spec/models/workshop_sponsor_spec.rb

@@ -6,18 +6,4 @@
         .with_message('already a sponsor')
     end
   end
-
-  context '#scopes' do
-    context '#hosts' do
-      it 'includes workshops with hosts' do
-        workshop_sponsor = Fabricate(:workshop_sponsor, host: true)
-
-        expect(WorkshopSponsor.hosts).to include(workshop_sponsor)
-      end
-
-      it 'excludes workshops without hosts' do
-        expect(WorkshopSponsor.hosts).to eq []
-      end
-    end
-  end
 end