Changes

opt: remove useless periodic CI jobs (#4081)

This pull request removes the CDC integration test jobs for both Kafka
and MySQL from the Tiflow project's CI/CD pipeline. It deletes the
associated Jenkins job DSL definitions, pipeline scripts, and Kubernetes
pod templates, as well as updates the Prow job configuration to stop
referencing these periodic jobs. This effectively disables the periodic
CDC integration tests for the `latest` branch of Tiflow.

**Removal of CDC Integration Test Jobs:**

* Deleted the Jenkins job DSL files for periodic CDC integration tests
for both Kafka and MySQL (`periodics_cdc_integration_kafka_test.groovy`
and `periodics_cdc_integration_mysql_test.groovy`).
[[1]](diffhunk://#diff-2bcf3c8848ae05f14bc177f1e87adc168569d4672f98298c20b34f9b3f239215L1-L38)
[[2]](diffhunk://#diff-5017bfbbf1bb1db27392316f87a26f40a3cfb6182451ccf0354dc1b21fa112d8L1-L38)
* Removed the corresponding pipeline scripts that defined the test logic
and stages for Kafka and MySQL CDC integration tests
(`periodics_cdc_integration_kafka_test.groovy` and
`periodics_cdc_integration_mysql_test.groovy` under
`pipelines/pingcap/tiflow/latest/`).
[[1]](diffhunk://#diff-2ddbe297da568f7227daeca36ca37d88518927cbd63cc72af5a436756bbf6d6eL1-L170)
[[2]](diffhunk://#diff-9707c40fa4184f8e31164b04234f040090c54427c22294a17f06fa4d8bfcfa0aL1-L170)

**Cleanup of Kubernetes Resources:**

* Deleted the Kubernetes pod templates used for running the CDC
integration tests for Kafka and MySQL
(`pod-periodics_cdc_integration_kafka_test.yaml` and
`pod-periodics_cdc_integration_mysql_test.yaml`).
[[1]](diffhunk://#diff-2225eae0c6cc4d4773aced5fec91e0f712d4c6697e08d5b704fca839df6c09acL1-L182)
[[2]](diffhunk://#diff-6bf89057fafc295ee9d2bcabc63cba16a4ebdb99406e53bd3ea81456c33236e2L1-L39)

**Prow Job Configuration Update:**

* Updated `prow-jobs/kustomization.yaml` to remove the reference to
`pingcap_tiflow_latest-periodics.yaml`, which included the removed
periodic jobs.
 (commit: c14bb55)