[Misc] Clean up deadcode for legacy processing pipeline

[Isotr0py]

Purpose

• Clean up some dead code for legacy pipeline

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
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (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 provides a cleanup of dead code related to a legacy processing pipeline. The changes include removing a workaround for empty multimodal inputs in a deprecated utility function, replacing it with an AssertionError to ensure the path is no longer taken. Additionally, a previously skipped test for an InternVL model is re-enabled, which is consistent with the removal of the legacy pipeline. The changes are well-contained and improve the overall health of the codebase.