Remove deprecated GetBlockV2 from Validator API

[gfukushima]

PR Description

This PR removes the GetBlockV2 from the Validator API. A follow-up PR will promote V3 to be the default.

Fixed Issue(s)

Part of #7779

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[greptile-apps]

PR Summary

This PR removes the deprecated GetBlockV2 from the Validator API, paving the way for GetBlockV3 to become the default.

• Removed /data/beaconrestapi/src/main/java/tech/pegasys/teku/beaconrestapi/handlers/v2/validator/GetNewBlock.java to eliminate the V2 endpoint.
• Deleted /data/beaconrestapi/src/test/java/tech/pegasys/teku/beaconrestapi/handlers/v2/validator/GetNewBlockV2Test.java to remove tests for the deprecated V2 API.
• Updated /data/beaconrestapi/src/main/java/tech/pegasys/teku/beaconrestapi/JsonTypeDefinitionBeaconRestApi.java to remove references to the V2 endpoint.
• Removed /data/beaconrestapi/src/integration-test/java/tech/pegasys/teku/beaconrestapi/v1/validator/GetNewBlockIntegrationTest.java as V2 tests are no longer needed.
• Updated CHANGELOG.md to document the removal of the deprecated GetBlockV2 endpoint.

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[gfukushima]

Closing this for now as the plans have changed, we want to enable V3 by default before removing V2