Remove load_balancing_disconnect_without_verify feature flag

This feature flag has been enabled on GitLab.com for a few days
and should be safe to removed now. On staging, we tested this by
shutting down several PgBouncer processes, and in production
we saw one case where a pod marked a host offline and later
came back.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/490104

Changelog: changed

config/feature_flags/gitlab_com_derisk/load_balancing_disconnect_without_verify.yml

----
-name: load_balancing_disconnect_without_verify
-feature_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/490211
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/166231
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/490104
-milestone: '17.5'
-group: infrastructure
-type: gitlab_com_derisk
-default_enabled: false

lib/gitlab/database/load_balancing/host.rb

@@ -112,9 +112,8 @@ def force_disconnect!
 
         def pool_disconnect!
           return pool.disconnect! if ::Gitlab.next_rails?
-          return pool.disconnect_without_verify! if Feature.enabled?(:load_balancing_disconnect_without_verify)
 
-          pool.disconnect!
+          pool.disconnect_without_verify!
         end
 
         def offline!

spec/lib/gitlab/database/load_balancing/host_spec.rb

@@ -87,16 +87,6 @@ def expect_next_replica_connection
     if ::Gitlab.next_rails?
       it_behaves_like 'disconnects the pool'
     else
-      context 'with load_balancing_disconnect_without_verify feature flag disabled' do
-        let(:disconnect_method) { :disconnect! }
-
-        before do
-          stub_feature_flags(load_balancing_disconnect_without_verify: false)
-        end
-
-        it_behaves_like 'disconnects the pool'
-      end
-
       context 'with load_balancing_disconnect_without_verify feature flag enabled' do
         let(:disconnect_method) { :disconnect_without_verify! }