Remove namespace select after group create fails during trial creation

...sets/javascripts/trials/components/namespace_selector.vue

ee/app/assets/javascripts/trials/init_namespace_selector.js

ee/app/controllers/trials_controller.rb

ee/app/views/trials/select_namespace_form.html.haml

...as/creation_with_multiple_existing_namespace_flow_spec.rb

...als/saas/creation_with_no_existing_namespace_flow_spec.rb

...pec/frontend/trials/components/namespace_selector_spec.js

ee/spec/support/helpers/features/trial_helpers.rb