Remove EE-specific usages of `:empty_project`

features/steps/group_hooks.rb

features/steps/project/elastic/project_search.rb

spec/controllers/ee/projects/boards_controller_spec.rb

spec/controllers/ee/projects_controller_spec.rb

spec/controllers/projects/approver_groups_controller_spec.rb

spec/controllers/projects/approvers_controller_spec.rb

spec/controllers/projects/issues_controller_ee_spec.rb

...s/projects/merge_requests/creations_controller_ee_spec.rb

spec/controllers/projects/mirrors_controller_spec.rb

spec/controllers/projects/push_rules_controller_spec.rb

spec/controllers/projects/settings/slacks_controller_spec.rb

spec/factories/audit_events.rb

spec/factories/forked_project_links.rb

spec/factories/geo/event_log.rb

spec/factories/geo/project_registry.rb

spec/factories/services.rb

spec/features/admin/admin_emails_spec.rb

spec/features/admin/admin_users_spec.rb

spec/features/boards/board_with_milestone_spec.rb

spec/features/boards/ee/boards_spec.rb