chore: remove the access codes feature flag

.env.test

@@ -3,7 +3,3 @@ KERNEL_CLASS='App\Kernel'
 # Fixed and committed so the test suite is reproducible, and never served: .env.test is excluded
 # from the deploy rsync and production takes APP_SECRET from its own uncommitted .env.local.
 APP_SECRET='$ecretf0rt3st'
-
-# The access-code suite tests the feature, not the gate in front of it, so it runs with the flag
-# on.
-FEATURE_ACCESS_CODES=true