[Feature] cleanup Istio flatbuffers when 1.24.0 is our minimum supported version

[kezhenxu94]

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• [X] I had searched in the issues and found no similar feature requirement.

Description

Clean up FlatBuffers and old metadata read method when 1.24.0 is our minimum supported version

Use case

No response

Related issues

#adapistio

Are you willing to submit a pull request to implement this on your own?

• [X] Yes I am willing to submit a pull request on my own!

Code of Conduct

• [X] I agree to follow this project's Code of Conduct

[wu-sheng]

We should plan to remove this in the first release of 2026, so roughly 10.5

[kezhenxu94]

Istio 1.24 will be ended at ~Aug 2025 (Expected), it’s better to have at least 6 months for users to upgrade, let’s consider this at the mid year of 2026