Use DELETE when signing out from registrar area

#599

spec/requests/registrar/sign_out_spec.rb

@@ -0,0 +1,20 @@
+require 'rails_helper'
+
+RSpec.describe 'Registrar area sign-out', settings: false do
+  describe 'sign-out' do
+    before do
+      sign_in_to_registrar_area
+    end
+
+    it 'signs the user out' do
+      delete registrar_destroy_user_session_path
+      follow_redirect!
+      expect(controller.current_user).to be_nil
+    end
+
+    it 'redirects to login url' do
+      delete registrar_destroy_user_session_path
+      expect(response).to redirect_to(registrar_login_url)
+    end
+  end
+end