[Task]: Remove Flink 1.14 and cleanup

[je-ik]

What needs to happen?

After #30789 we can remove support for Flink 1.14 and review code to do cleanup of unneeded version specific code in runners/flink/<version>/src.

Issue Priority

Priority: 3 (nice-to-have improvement)

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