Simplify login for officer user in tests

The same way it's done in other places. We also remove a useless
assignment.

spec/features/budget_polls/officing_spec.rb

@@ -5,13 +5,11 @@ describe "Budget Poll Officing" do
   scenario "Show sidebar menus if officer has shifts assigned" do
     booth = create(:poll_booth)
     booth_assignment = create(:poll_booth_assignment, booth: booth)
-
-    user = create(:user)
-    officer = create(:poll_officer, user: user)
+    officer = create(:poll_officer)
 
     create(:poll_shift, officer: officer, booth: booth, date: Date.current, task: :vote_collection)
 
-    login_as user
+    login_as officer.user
     visit officing_root_path
 
     expect(page).not_to have_content("You don't have officing shifts today")
@@ -32,10 +30,8 @@ describe "Budget Poll Officing" do
   end
 
   scenario "Do not show sidebar menus if officer has no shifts assigned" do
-    user = create(:user)
-    officer = create(:poll_officer, user: user)
+    login_as(create(:poll_officer).user)
 
-    login_as user
     visit officing_root_path
 
     expect(page).to have_content("You don't have officing shifts today")