Expect less transaction for identity destroy service

According to the specs description the behavior is correct
now and there is no need in expecting an additional transaction
to be raised

ee/spec/services/group_saml/identity/destroy_service_spec.rb

@@ -18,13 +18,13 @@ RSpec.describe GroupSaml::Identity::DestroyService do
   end
 
   it "does not use a transaction" do
-    expect(::Identity).to receive(:transaction).and_yield.once
+    expect(::Identity).not_to receive(:transaction)
 
     subject.execute
   end
 
   it "uses a transaction when transactional is set" do
-    expect(::Identity).to receive(:transaction).and_yield.twice
+    expect(::Identity).to receive(:transaction).and_yield.once
 
     subject.execute(transactional: true)
   end