[V0 deprecation] Remove platform v1 controling interface

[Isotr0py]

Purpose

• Since V0 has been removed, I think there is no need to keep supports_v1 and default_v1 to control v0 fallback at platform level

Also cc @Yikun @xuechendi in case these interfaces are still used by plugins.

Test Plan

Test Result

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
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• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request removes the supports_v1 and default_v1 methods from the platform interfaces, aiming to clean up V0 deprecation-related code. The changes are consistent across the codebase, removing the method definitions and their usages. However, this change removes a safeguard that prevented V1 from being enabled on new or untested platforms. I've raised a critical concern about the potential for enabling V1 on incompatible platforms, which could lead to runtime issues. It's important to clarify whether V0 is fully removed, as this would dictate whether more V0-related fallback logic should be cleaned up, or if a new safeguard is needed.