Move redirection test to controller specs

We make the test faster and avoid a strange issue with `current_path` in
JavaScript tests.

We should probably have done this in commit ec1874325.

spec/controllers/legislation/proposals_controller_spec.rb

@@ -0,0 +1,11 @@
+require "rails_helper"
+
+describe Legislation::ProposalsController do
+  describe "GET new" do
+    it "redirects to register path if user is not logged in" do
+      get :new, params: { process_id: create(:legislation_process, :in_proposals_phase).id }
+
+      expect(response).to redirect_to new_user_session_path
+    end
+  end
+end

spec/system/legislation/processes_spec.rb

@@ -387,16 +387,6 @@ describe "Legislation" do
         expect(page).to have_content("There are no proposals")
       end
 
-      scenario "create proposal button redirects to register path if user is not logged in" do
-        process = create(:legislation_process, :in_proposals_phase)
-
-        visit legislation_process_proposals_path(process)
-        click_link "Create a proposal"
-
-        expect(page).to have_current_path new_user_session_path
-        expect(page).to have_content "You must sign in or register to continue"
-      end
-
       include_examples "not published permissions", :legislation_process_proposals_path
     end