[Task]: Reverse it component migration

### What needs to happen?

it/ components were migrated from DataflowTemplate repository but never worked in Beam repository.

- https://github.com/apache/beam/actions/workflows/beam_PostCommit_Java_IO_Performance_Tests.yml?query=event%3Aschedule has never worked

- changes on it/ keep going in DataflowTemplate, see [template it history](https://github.com/GoogleCloudPlatform/DataflowTemplates/commits/main/it) and [Beam it history]( https://github.com/apache/beam/commits/master/it). In particular:

- it-gcp exists in both repositories and decoupled. We tried to sync the code a few times before release cut, but fully migration yet happened.

- Moreover, it was later find necessary to copy fully migrated modules (deleted in DataflowTemplates) back, e.g. in https://github.com/GoogleCloudPlatform/DataflowTemplates/pull/826 it/conditions and it/jdbc were copied back; in https://github.com/GoogleCloudPlatform/DataflowTemplates/pull/1312 it/splunk is going to copy back

It is now clear these modules should really live in DataflowTemplate repo. Instead of advice developers to try it/ module that never successfully run in Beam repo, we should return them to where it lives

### Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

### Issue Components

- [ ] Component: Python SDK
- [ ] Component: Java SDK
- [ ] Component: Go SDK
- [ ] Component: Typescript SDK
- [ ] Component: IO connector
- [ ] Component: Beam YAML
- [ ] Component: Beam examples
- [ ] Component: Beam playground
- [ ] Component: Beam katas
- [ ] Component: Website
- [ ] Component: Spark Runner
- [ ] Component: Flink Runner
- [ ] Component: Samza Runner
- [ ] Component: Twister2 Runner
- [ ] Component: Hazelcast Jet Runner
- [ ] Component: Google Cloud Dataflow Runner